Add m-esr52 at 52.6.0

14 files changed, 1963 insertions, 0 deletions

diff --git a/js/src/threading/ConditionVariable.h b/js/src/threading/ConditionVariable.h
new file mode 100644
index 0000000000..f1c9a906c9
--- /dev/null
+++ b/js/src/threading/ConditionVariable.h
@@ -0,0 +1,121 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef threading_ConditionVariable_h
+#define threading_ConditionVariable_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Move.h"
+#include "mozilla/TimeStamp.h"
+
+#include <stdint.h>
+#ifndef XP_WIN
+# include <pthread.h>
+#endif
+
+#include "threading/LockGuard.h"
+#include "threading/Mutex.h"
+
+namespace js {
+
+template <typename T> using UniqueLock = LockGuard<T>;
+
+enum class CVStatus {
+  NoTimeout,
+  Timeout
+};
+
+// A poly-fill for std::condition_variable.
+class ConditionVariable
+{
+public:
+  struct PlatformData;
+
+  ConditionVariable();
+  ~ConditionVariable();
+
+  // Wake one thread that is waiting on this condition.
+  void notify_one();
+
+  // Wake all threads that are waiting on this condition.
+  void notify_all();
+
+  // Block the current thread of execution until this condition variable is
+  // woken from another thread via notify_one or notify_all.
+  void wait(UniqueLock<Mutex>& lock);
+
+  // As with |wait|, block the current thread of execution until woken from
+  // another thread. This method will resume waiting once woken until the given
+  // Predicate |pred| evaluates to true.
+  template <typename Predicate>
+  void wait(UniqueLock<Mutex>& lock, Predicate pred) {
+    while (!pred()) {
+      wait(lock);
+    }
+  }
+
+  // Block the current thread of execution until woken from another thread, or
+  // the given absolute time is reached. The given absolute time is evaluated
+  // when this method is called, so will wake up after (abs_time - now),
+  // independent of system clock changes. While insulated from clock changes,
+  // this API is succeptible to the issues discussed above wait_for.
+  CVStatus wait_until(UniqueLock<Mutex>& lock,
+                      const mozilla::TimeStamp& abs_time);
+
+  // As with |wait_until|, block the current thread of execution until woken
+  // from another thread, or the given absolute time is reached. This method
+  // will resume waiting once woken until the given Predicate |pred| evaluates
+  // to true.
+  template <typename Predicate>
+  bool wait_until(UniqueLock<Mutex>& lock, const mozilla::TimeStamp& abs_time,
+                  Predicate pred) {
+    while (!pred()) {
+      if (wait_until(lock, abs_time) == CVStatus::Timeout) {
+        return pred();
+      }
+    }
+    return true;
+  }
+
+  // Block the current thread of execution until woken from another thread, or
+  // the given time duration has elapsed. Given that the system may be
+  // interrupted between the callee and the actual wait beginning, this call
+  // has a minimum granularity of the system's scheduling interval, and may
+  // encounter substantially longer delays, depending on system load.
+  CVStatus wait_for(UniqueLock<Mutex>& lock,
+                    const mozilla::TimeDuration& rel_time);
+
+  // As with |wait_for|, block the current thread of execution until woken from
+  // another thread or the given time duration has elapsed. This method will
+  // resume waiting once woken until the given Predicate |pred| evaluates to
+  // true.
+  template <typename Predicate>
+  bool wait_for(UniqueLock<Mutex>& lock, const mozilla::TimeDuration& rel_time,
+                Predicate pred) {
+    return wait_until(lock, mozilla::TimeStamp::Now() + rel_time,
+                      mozilla::Move(pred));
+  }
+
+
+private:
+  ConditionVariable(const ConditionVariable&) = delete;
+  ConditionVariable& operator=(const ConditionVariable&) = delete;
+
+  PlatformData* platformData();
+
+#ifndef XP_WIN
+  void* platformData_[sizeof(pthread_cond_t) / sizeof(void*)];
+  static_assert(sizeof(pthread_cond_t) / sizeof(void*) != 0 &&
+                sizeof(pthread_cond_t) % sizeof(void*) == 0,
+                "pthread_cond_t must have pointer alignment");
+#else
+  void* platformData_[4];
+#endif
+};
+
+} // namespace js
+
+#endif // threading_ConditionVariable_h
diff --git a/js/src/threading/ExclusiveData.h b/js/src/threading/ExclusiveData.h
new file mode 100644
index 0000000000..732ef91d6f
--- /dev/null
+++ b/js/src/threading/ExclusiveData.h
@@ -0,0 +1,197 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef threading_ExclusiveData_h
+#define threading_ExclusiveData_h
+
+#include "mozilla/Alignment.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Move.h"
+
+#include "threading/Mutex.h"
+
+namespace js {
+
+/**
+ * A mutual exclusion lock class.
+ *
+ * `ExclusiveData` provides an RAII guard to automatically lock and unlock when
+ * accessing the protected inner value.
+ *
+ * Unlike the STL's `std::mutex`, the protected value is internal to this
+ * class. This is a huge win: one no longer has to rely on documentation to
+ * explain the relationship between a lock and its protected data, and the type
+ * system can enforce[0] it.
+ *
+ * For example, suppose we have a counter class:
+ *
+ *     class Counter
+ *     {
+ *         int32_t i;
+ *
+ *       public:
+ *         void inc(int32_t n) { i += n; }
+ *     };
+ *
+ * If we share a counter across threads with `std::mutex`, we rely solely on
+ * comments to document the relationship between the lock and its data, like
+ * this:
+ *
+ *     class SharedCounter
+ *     {
+ *         // Remember to acquire `counter_lock` when accessing `counter`,
+ *         // pretty please!
+ *         Counter counter;
+ *         std::mutex counter_lock;
+ *
+ *       public:
+ *         void inc(size_t n) {
+ *             // Whoops, forgot to acquire the lock! Off to the races!
+ *             counter.inc(n);
+ *         }
+ *     };
+ *
+ * In contrast, `ExclusiveData` wraps the protected value, enabling the type
+ * system to enforce that we acquire the lock before accessing the value:
+ *
+ *     class SharedCounter
+ *     {
+ *         ExclusiveData<Counter> counter;
+ *
+ *       public:
+ *         void inc(size_t n) {
+ *             auto guard = counter.lock();
+ *             guard->inc(n);
+ *         }
+ *     };
+ *
+ * The API design is based on Rust's `std::sync::Mutex<T>` type.
+ *
+ * [0]: Of course, we don't have a borrow checker in C++, so the type system
+ *      cannot guarantee that you don't stash references received from
+ *      `ExclusiveData<T>::Guard` somewhere such that the reference outlives the
+ *      guard's lifetime and therefore becomes invalid. To help avoid this last
+ *      foot-gun, prefer using the guard directly! Do not store raw references
+ *      to the protected value in other structures!
+ */
+template <typename T>
+class ExclusiveData
+{
+    mutable Mutex lock_;
+    mutable mozilla::AlignedStorage2<T> value_;
+
+    ExclusiveData(const ExclusiveData&) = delete;
+    ExclusiveData& operator=(const ExclusiveData&) = delete;
+
+    void acquire() const { lock_.lock(); }
+    void release() const { lock_.unlock(); }
+
+  public:
+    /**
+     * Create a new `ExclusiveData`, with perfect forwarding of the protected
+     * value.
+     */
+    template <typename U>
+    explicit ExclusiveData(const MutexId& id, U&& u)
+      : lock_(id)
+    {
+        new (value_.addr()) T(mozilla::Forward<U>(u));
+    }
+
+    /**
+     * Create a new `ExclusiveData`, constructing the protected value in place.
+     */
+    template <typename... Args>
+    explicit ExclusiveData(const MutexId& id, Args&&... args)
+      : lock_(id)
+    {
+        new (value_.addr()) T(mozilla::Forward<Args>(args)...);
+    }
+
+    ~ExclusiveData() {
+        acquire();
+        value_.addr()->~T();
+        release();
+    }
+
+    ExclusiveData(ExclusiveData&& rhs) :
+      lock_(mozilla::Move(rhs.lock))
+    {
+        MOZ_ASSERT(&rhs != this, "self-move disallowed!");
+        new (value_.addr()) T(mozilla::Move(*rhs.value_.addr()));
+    }
+
+    ExclusiveData& operator=(ExclusiveData&& rhs) {
+        this->~ExclusiveData();
+        new (this) ExclusiveData(mozilla::Move(rhs));
+        return *this;
+    }
+
+    /**
+     * An RAII class that provides exclusive access to a `ExclusiveData<T>`'s
+     * protected inner `T` value.
+     *
+     * Note that this is intentionally marked MOZ_STACK_CLASS instead of
+     * MOZ_RAII_CLASS, as the latter disallows moves and returning by value, but
+     * Guard utilizes both.
+     */
+    class MOZ_STACK_CLASS Guard
+    {
+        const ExclusiveData* parent_;
+
+        Guard(const Guard&) = delete;
+        Guard& operator=(const Guard&) = delete;
+
+      public:
+        explicit Guard(const ExclusiveData& parent)
+          : parent_(&parent)
+        {
+            parent_->acquire();
+        }
+
+        Guard(Guard&& rhs)
+          : parent_(rhs.parent_)
+        {
+            MOZ_ASSERT(&rhs != this, "self-move disallowed!");
+            rhs.parent_ = nullptr;
+        }
+
+        Guard& operator=(Guard&& rhs) {
+            this->~Guard();
+            new (this) Guard(mozilla::Move(rhs));
+            return *this;
+        }
+
+        T& get() const {
+            MOZ_ASSERT(parent_);
+            return *parent_->value_.addr();
+        }
+
+        operator T& () const { return get(); }
+        T* operator->() const { return &get(); }
+
+        const ExclusiveData<T>* parent() const {
+            MOZ_ASSERT(parent_);
+            return parent_;
+        }
+
+        ~Guard() {
+            if (parent_)
+                parent_->release();
+        }
+    };
+
+    /**
+     * Access the protected inner `T` value for exclusive reading and writing.
+     */
+    Guard lock() const {
+        return Guard(*this);
+    }
+};
+
+} // namespace js
+
+#endif // threading_ExclusiveData_h
diff --git a/js/src/threading/LockGuard.h b/js/src/threading/LockGuard.h
new file mode 100644
index 0000000000..45b023a90a
--- /dev/null
+++ b/js/src/threading/LockGuard.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef threading_LockGuard_h
+#define threading_LockGuard_h
+
+namespace js {
+
+template <typename Mutex> class MOZ_RAII UnlockGuard;
+
+template <typename Mutex>
+class MOZ_RAII LockGuard
+{
+  friend class UnlockGuard<Mutex>;
+  friend class ConditionVariable;
+  Mutex& lock;
+
+public:
+  explicit LockGuard(Mutex& aLock)
+    : lock(aLock)
+  {
+    lock.lock();
+  }
+
+  ~LockGuard() {
+    lock.unlock();
+  }
+};
+
+template <typename Mutex>
+class MOZ_RAII UnlockGuard
+{
+  Mutex& lock;
+
+public:
+  explicit UnlockGuard(LockGuard<Mutex>& aGuard)
+    : lock(aGuard.lock)
+  {
+    lock.unlock();
+  }
+
+  ~UnlockGuard() {
+    lock.lock();
+  }
+};
+
+} // namespace js
+
+#endif // threading_LockGuard_h
diff --git a/js/src/threading/Mutex.cpp b/js/src/threading/Mutex.cpp
new file mode 100644
index 0000000000..154129dee0
--- /dev/null
+++ b/js/src/threading/Mutex.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "threading/Mutex.h"
+
+#include "js/Utility.h"
+
+using namespace js;
+
+#ifdef DEBUG
+
+MOZ_THREAD_LOCAL(js::Mutex::MutexVector*) js::Mutex::HeldMutexStack;
+
+/* static */ bool
+js::Mutex::Init()
+{
+  return HeldMutexStack.init();
+}
+
+/* static */ void
+js::Mutex::ShutDown()
+{
+  js_delete(HeldMutexStack.get());
+  HeldMutexStack.set(nullptr);
+}
+
+/* static */ js::Mutex::MutexVector&
+js::Mutex::heldMutexStack()
+{
+  auto stack = HeldMutexStack.get();
+  if (!stack) {
+    AutoEnterOOMUnsafeRegion oomUnsafe;
+    stack = js_new<MutexVector>();
+    if (!stack)
+      oomUnsafe.crash("js::Mutex::heldMutexStack");
+    HeldMutexStack.set(stack);
+  }
+  return *stack;
+}
+
+void
+js::Mutex::lock()
+{
+  auto& stack = heldMutexStack();
+  if (!stack.empty()) {
+    const Mutex& prev = *stack.back();
+    if (id_.order <= prev.id_.order) {
+      fprintf(stderr,
+              "Attempt to acquire mutex %s with order %d while holding %s with order %d\n",
+              id_.name, id_.order, prev.id_.name, prev.id_.order);
+      MOZ_CRASH("Mutex ordering violation");
+    }
+  }
+
+  MutexImpl::lock();
+
+  AutoEnterOOMUnsafeRegion oomUnsafe;
+  if (!stack.append(this))
+    oomUnsafe.crash("js::Mutex::lock");
+}
+
+void
+js::Mutex::unlock()
+{
+  auto& stack = heldMutexStack();
+  MOZ_ASSERT(stack.back() == this);
+  MutexImpl::unlock();
+  stack.popBack();
+}
+
+#endif
diff --git a/js/src/threading/Mutex.h b/js/src/threading/Mutex.h
new file mode 100644
index 0000000000..1ea019dde8
--- /dev/null
+++ b/js/src/threading/Mutex.h
@@ -0,0 +1,128 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef threading_Mutex_h
+#define threading_Mutex_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Move.h"
+#include "mozilla/ThreadLocal.h"
+#include "mozilla/Vector.h"
+
+#include <new>
+#include <string.h>
+
+namespace js {
+
+class ConditionVariable;
+
+namespace detail {
+
+class MutexImpl
+{
+public:
+  struct PlatformData;
+
+  MutexImpl();
+  ~MutexImpl();
+
+  MutexImpl(MutexImpl&& rhs)
+    : platformData_(rhs.platformData_)
+  {
+    MOZ_ASSERT(this != &rhs, "self move disallowed!");
+    rhs.platformData_ = nullptr;
+  }
+
+  MutexImpl& operator=(MutexImpl&& rhs) {
+    this->~MutexImpl();
+    new (this) MutexImpl(mozilla::Move(rhs));
+    return *this;
+  }
+
+  bool operator==(const MutexImpl& rhs) {
+    return platformData_ == rhs.platformData_;
+  }
+
+protected:
+  void lock();
+  void unlock();
+
+private:
+  MutexImpl(const MutexImpl&) = delete;
+  void operator=(const MutexImpl&) = delete;
+
+  friend class js::ConditionVariable;
+  PlatformData* platformData() {
+    MOZ_ASSERT(platformData_);
+    return platformData_;
+  };
+
+  PlatformData* platformData_;
+};
+
+} // namespace detail
+
+// A MutexId secifies the name and mutex order for a mutex.
+//
+// The mutex order defines the allowed order of mutex acqusition on a single
+// thread. Mutexes must be acquired in strictly increasing order. Mutexes with
+// the same order may not be held at the same time by that thread.
+struct MutexId
+{
+  const char* name;
+  uint32_t order;
+};
+
+#ifndef DEBUG
+
+class Mutex : public detail::MutexImpl
+{
+public:
+  static bool Init() { return true; }
+  static void ShutDown() {}
+
+  explicit Mutex(const MutexId& id) {}
+
+  using MutexImpl::lock;
+  using MutexImpl::unlock;
+};
+
+#else
+
+// In debug builds, js::Mutex is a wrapper over MutexImpl that checks correct
+// locking order is observed.
+//
+// The class maintains a per-thread stack of currently-held mutexes to enable it
+// to check this.
+class Mutex : public detail::MutexImpl
+{
+public:
+  static bool Init();
+  static void ShutDown();
+
+  explicit Mutex(const MutexId& id)
+   : id_(id)
+  {
+    MOZ_ASSERT(id_.order != 0);
+  }
+
+  void lock();
+  void unlock();
+
+private:
+  const MutexId id_;
+
+  using MutexVector = mozilla::Vector<const Mutex*>;
+  static MOZ_THREAD_LOCAL(MutexVector*) HeldMutexStack;
+  static MutexVector& heldMutexStack();
+};
+
+#endif
+
+} // namespace js
+
+#endif // threading_Mutex_h
diff --git a/js/src/threading/Thread.h b/js/src/threading/Thread.h
new file mode 100644
index 0000000000..2ea445e7da
--- /dev/null
+++ b/js/src/threading/Thread.h
@@ -0,0 +1,243 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef threading_Thread_h
+#define threading_Thread_h
+
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/IndexSequence.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/Tuple.h"
+
+#include <stdint.h>
+
+#include "js/Utility.h"
+
+#ifdef XP_WIN
+# define THREAD_RETURN_TYPE unsigned int
+# define THREAD_CALL_API __stdcall
+#else
+# define THREAD_RETURN_TYPE void*
+# define THREAD_CALL_API
+#endif
+
+namespace js {
+namespace detail {
+template <typename F, typename... Args>
+class ThreadTrampoline;
+} // namespace detail
+
+// Execute the given functor concurrent with the currently executing instruction
+// stream and within the current address space. Use with care.
+class Thread
+{
+public:
+  struct Hasher;
+
+  class Id
+  {
+    friend struct Hasher;
+    class PlatformData;
+    void* platformData_[2];
+
+  public:
+    Id();
+
+    Id(const Id&) = default;
+    Id(Id&&) = default;
+    Id& operator=(const Id&) = default;
+    Id& operator=(Id&&) = default;
+
+    bool operator==(const Id& aOther) const;
+    bool operator!=(const Id& aOther) const { return !operator==(aOther); }
+
+    inline PlatformData* platformData();
+    inline const PlatformData* platformData() const;
+  };
+
+  // Provides optional parameters to a Thread.
+  class Options
+  {
+    size_t stackSize_;
+
+  public:
+    Options() : stackSize_(0) {}
+
+    Options& setStackSize(size_t sz) { stackSize_ = sz; return *this; }
+    size_t stackSize() const { return stackSize_; }
+  };
+
+  // A js::HashTable hash policy for keying hash tables by js::Thread::Id.
+  struct Hasher
+  {
+    typedef Id Lookup;
+
+    static HashNumber hash(const Lookup& l);
+
+    static bool match(const Id& key, const Lookup& lookup) {
+      return key == lookup;
+    }
+  };
+
+  // Create a Thread in an initially unjoinable state. A thread of execution can
+  // be created for this Thread by calling |init|. Some of the thread's
+  // properties may be controlled by passing options to this constructor.
+  template <typename O = Options,
+            // SFINAE to make sure we don't try and treat functors for the other
+            // constructor as an Options and vice versa.
+            typename NonConstO = typename mozilla::RemoveConst<O>::Type,
+            typename DerefO = typename mozilla::RemoveReference<NonConstO>::Type,
+            typename = typename mozilla::EnableIf<mozilla::IsSame<DerefO, Options>::value,
+                                                  void*>::Type>
+  explicit Thread(O&& options = Options())
+    : id_(Id())
+    , options_(mozilla::Forward<O>(options))
+  { }
+
+  // Start a thread of execution at functor |f| with parameters |args|. This
+  // method will return false if thread creation fails. This Thread must not
+  // already have been created. Note that the arguments must be either POD or
+  // rvalue references (mozilla::Move). Attempting to pass a reference will
+  // result in the value being copied, which may not be the intended behavior.
+  // See the comment below on ThreadTrampoline::args for an explanation.
+  template <typename F, typename... Args>
+  MOZ_MUST_USE bool init(F&& f, Args&&... args) {
+    MOZ_RELEASE_ASSERT(!joinable());
+    using Trampoline = detail::ThreadTrampoline<F, Args...>;
+    AutoEnterOOMUnsafeRegion oom;
+    auto trampoline = js_new<Trampoline>(mozilla::Forward<F>(f),
+                                         mozilla::Forward<Args>(args)...);
+    if (!trampoline)
+      oom.crash("js::Thread::init");
+    return create(Trampoline::Start, trampoline);
+  }
+
+  // The thread must be joined or detached before destruction.
+  ~Thread() {
+    MOZ_RELEASE_ASSERT(!joinable());
+  }
+
+  // Move the thread into the detached state without blocking. In the detatched
+  // state, the thread continues to run until it exits, but cannot be joined.
+  // After this method returns, this Thread no longer represents a thread of
+  // execution. When the thread exits, its resources will be cleaned up by the
+  // system. At process exit, if the thread is still running, the thread's TLS
+  // storage will be destructed, but the thread stack will *not* be unrolled.
+  void detach();
+
+  // Block the current thread until this Thread returns from the functor it was
+  // created with. The thread's resources will be cleaned up before this
+  // function returns. After this method returns, this Thread no longer
+  // represents a thread of execution.
+  void join();
+
+  // Return true if this thread has not yet been joined or detached. If this
+  // method returns false, this Thread does not have an associated thread of
+  // execution, for example, if it has been previously moved or joined.
+  bool joinable() const {
+    return get_id() != Id();
+  }
+
+  // Returns the id of this thread if this represents a thread of execution or
+  // the default constructed Id() if not. The thread ID is guaranteed to
+  // uniquely identify a thread and can be compared with the == operator.
+  Id get_id() const { return id_; }
+
+  // Allow threads to be moved so that they can be stored in containers.
+  Thread(Thread&& aOther);
+  Thread& operator=(Thread&& aOther);
+
+private:
+  // Disallow copy as that's not sensible for unique resources.
+  Thread(const Thread&) = delete;
+  void operator=(const Thread&) = delete;
+
+  // Provide a process global ID to each thread.
+  Id id_;
+
+  // Overridable thread creation options.
+  Options options_;
+
+  // Dispatch to per-platform implementation of thread creation.
+  MOZ_MUST_USE bool create(THREAD_RETURN_TYPE (THREAD_CALL_API *aMain)(void*), void* aArg);
+};
+
+namespace ThisThread {
+
+// Return the thread id of the calling thread.
+Thread::Id GetId();
+
+// Set the current thread name. Note that setting the thread name may not be
+// available on all platforms; on these platforms setName() will simply do
+// nothing.
+void SetName(const char* name);
+
+// Get the current thread name. As with SetName, not available on all
+// platforms. On these platforms getName() will give back an empty string (by
+// storing NUL in nameBuffer[0]). 'len' is the bytes available to be written in
+// 'nameBuffer', including the terminating NUL.
+void GetName(char* nameBuffer, size_t len);
+
+} // namespace ThisThread
+
+namespace detail {
+
+// Platform thread APIs allow passing a single void* argument to the target
+// thread. This class is responsible for safely ferrying the arg pack and
+// functor across that void* membrane and running it in the other thread.
+template <typename F, typename... Args>
+class ThreadTrampoline
+{
+  // The functor to call.
+  F f;
+
+  // A std::decay copy of the arguments, as specified by std::thread. Using an
+  // rvalue reference for the arguments to Thread and ThreadTrampoline gives us
+  // move semantics for large structures, allowing us to quickly and easily pass
+  // enormous amounts of data to a new thread. Unfortunately, there is a
+  // downside: rvalue references becomes lvalue references when used with POD
+  // types. This becomes dangerous when attempting to pass POD stored on the
+  // stack to the new thread; the rvalue reference will implicitly become an
+  // lvalue reference to the stack location. Thus, the value may not exist if
+  // the parent thread leaves the frame before the read happens in the new
+  // thread. To avoid this dangerous and highly non-obvious footgun, the
+  // standard requires a "decay" copy of the arguments at the cost of making it
+  // impossible to pass references between threads.
+  mozilla::Tuple<typename mozilla::Decay<Args>::Type...> args;
+
+public:
+  // Note that this template instatiation duplicates and is identical to the
+  // class template instantiation. It is required for perfect forwarding of
+  // rvalue references, which is only enabled for calls to a function template,
+  // even if the class template arguments are correct.
+  template <typename G, typename... ArgsT>
+  explicit ThreadTrampoline(G&& aG, ArgsT&&... aArgsT)
+    : f(mozilla::Forward<F>(aG)),
+      args(mozilla::Forward<Args>(aArgsT)...)
+  {
+  }
+
+  static THREAD_RETURN_TYPE THREAD_CALL_API Start(void* aPack) {
+    auto* pack = static_cast<ThreadTrampoline<F, Args...>*>(aPack);
+    pack->callMain(typename mozilla::IndexSequenceFor<Args...>::Type());
+    js_delete(pack);
+    return 0;
+  }
+
+  template<size_t ...Indices>
+  void callMain(mozilla::IndexSequence<Indices...>) {
+    f(mozilla::Get<Indices>(args)...);
+  }
+};
+
+} // namespace detail
+} // namespace js
+
+#undef THREAD_RETURN_TYPE
+
+#endif // threading_Thread_h
diff --git a/js/src/threading/posix/ConditionVariable.cpp b/js/src/threading/posix/ConditionVariable.cpp
new file mode 100644
index 0000000000..35a90c604c
--- /dev/null
+++ b/js/src/threading/posix/ConditionVariable.cpp
@@ -0,0 +1,180 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/Assertions.h"
+#include "mozilla/CheckedInt.h"
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "threading/ConditionVariable.h"
+#include "threading/Mutex.h"
+#include "threading/posix/MutexPlatformData.h"
+
+using mozilla::CheckedInt;
+using mozilla::TimeDuration;
+using mozilla::TimeStamp;
+
+static const long NanoSecPerSec = 1000000000;
+
+// Android 32-bit & macOS 10.12 has the clock functions, but not pthread_condattr_setclock.
+#if defined(HAVE_CLOCK_MONOTONIC) && \
+    !(defined(__ANDROID__) && !defined(__LP64__)) && !defined(__APPLE__)
+# define USE_CLOCK_API
+#endif
+
+#ifdef USE_CLOCK_API
+// The C++ specification defines std::condition_variable::wait_for in terms of
+// std::chrono::steady_clock, which is closest to CLOCK_MONOTONIC.
+static const clockid_t WhichClock = CLOCK_MONOTONIC;
+
+// While timevaladd is widely available to work with timevals, the newer
+// timespec structure is largely lacking such conveniences. Thankfully, the
+// utilities available in MFBT make implementing our own quite easy.
+static void
+moz_timespecadd(struct timespec* lhs, struct timespec* rhs, struct timespec* result)
+{
+  // Add nanoseconds. This may wrap, but not above 2 billion.
+  MOZ_RELEASE_ASSERT(lhs->tv_nsec < NanoSecPerSec);
+  MOZ_RELEASE_ASSERT(rhs->tv_nsec < NanoSecPerSec);
+  result->tv_nsec = lhs->tv_nsec + rhs->tv_nsec;
+
+  // Add seconds, checking for overflow in the platform specific time_t type.
+  CheckedInt<time_t> sec = CheckedInt<time_t>(lhs->tv_sec) + rhs->tv_sec;
+
+  // If nanoseconds overflowed, carry the result over into seconds.
+  if (result->tv_nsec >= NanoSecPerSec) {
+    MOZ_RELEASE_ASSERT(result->tv_nsec < 2 * NanoSecPerSec);
+    result->tv_nsec -= NanoSecPerSec;
+    sec += 1;
+  }
+
+  // Extracting the value asserts that there was no overflow.
+  MOZ_RELEASE_ASSERT(sec.isValid());
+  result->tv_sec = sec.value();
+}
+#endif
+
+struct js::ConditionVariable::PlatformData
+{
+  pthread_cond_t ptCond;
+};
+
+js::ConditionVariable::ConditionVariable()
+{
+  pthread_cond_t* ptCond = &platformData()->ptCond;
+
+#ifdef USE_CLOCK_API
+  pthread_condattr_t attr;
+  int r0 = pthread_condattr_init(&attr);
+  MOZ_RELEASE_ASSERT(!r0);
+
+  int r1 = pthread_condattr_setclock(&attr, WhichClock);
+  MOZ_RELEASE_ASSERT(!r1);
+
+  int r2 = pthread_cond_init(ptCond, &attr);
+  MOZ_RELEASE_ASSERT(!r2);
+
+  int r3 = pthread_condattr_destroy(&attr);
+  MOZ_RELEASE_ASSERT(!r3);
+#else
+  int r = pthread_cond_init(ptCond, NULL);
+  MOZ_RELEASE_ASSERT(!r);
+#endif
+}
+
+js::ConditionVariable::~ConditionVariable()
+{
+  int r = pthread_cond_destroy(&platformData()->ptCond);
+  MOZ_RELEASE_ASSERT(r == 0);
+}
+
+void
+js::ConditionVariable::notify_one()
+{
+  int r = pthread_cond_signal(&platformData()->ptCond);
+  MOZ_RELEASE_ASSERT(r == 0);
+}
+
+void
+js::ConditionVariable::notify_all()
+{
+  int r = pthread_cond_broadcast(&platformData()->ptCond);
+  MOZ_RELEASE_ASSERT(r == 0);
+}
+
+void
+js::ConditionVariable::wait(UniqueLock<Mutex>& lock)
+{
+  pthread_cond_t* ptCond = &platformData()->ptCond;
+  pthread_mutex_t* ptMutex = &lock.lock.platformData()->ptMutex;
+
+  int r = pthread_cond_wait(ptCond, ptMutex);
+  MOZ_RELEASE_ASSERT(r == 0);
+}
+
+js::CVStatus
+js::ConditionVariable::wait_until(UniqueLock<Mutex>& lock,
+                                  const TimeStamp& abs_time)
+{
+  return wait_for(lock, abs_time - TimeStamp::Now());
+}
+
+js::CVStatus
+js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
+                                const TimeDuration& a_rel_time)
+{
+  if (a_rel_time == TimeDuration::Forever()) {
+    wait(lock);
+    return CVStatus::NoTimeout;
+  }
+
+  pthread_cond_t* ptCond = &platformData()->ptCond;
+  pthread_mutex_t* ptMutex = &lock.lock.platformData()->ptMutex;
+  int r;
+
+  // Clamp to 0, as time_t is unsigned.
+  TimeDuration rel_time = a_rel_time < TimeDuration::FromSeconds(0)
+                          ? TimeDuration::FromSeconds(0)
+                          : a_rel_time;
+
+  // Convert the duration to a timespec.
+  struct timespec rel_ts;
+  rel_ts.tv_sec = static_cast<time_t>(rel_time.ToSeconds());
+  rel_ts.tv_nsec = static_cast<uint64_t>(rel_time.ToMicroseconds() * 1000.0) % NanoSecPerSec;
+
+#ifdef USE_CLOCK_API
+  struct timespec now_ts;
+  r = clock_gettime(WhichClock, &now_ts);
+  MOZ_RELEASE_ASSERT(!r);
+
+  struct timespec abs_ts;
+  moz_timespecadd(&now_ts, &rel_ts, &abs_ts);
+
+  r = pthread_cond_timedwait(ptCond, ptMutex, &abs_ts);
+#else
+  // Our non-clock-supporting platforms, OS X and Android, do support waiting
+  // on a condition variable with a relative timeout.
+  r = pthread_cond_timedwait_relative_np(ptCond, ptMutex, &rel_ts);
+#endif
+
+  if (r == 0) {
+    return CVStatus::NoTimeout;
+  }
+  MOZ_RELEASE_ASSERT(r == ETIMEDOUT);
+  return CVStatus::Timeout;
+}
+
+js::ConditionVariable::PlatformData*
+js::ConditionVariable::platformData()
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}
diff --git a/js/src/threading/posix/MutexImpl.cpp b/js/src/threading/posix/MutexImpl.cpp
new file mode 100644
index 0000000000..1d406400fa
--- /dev/null
+++ b/js/src/threading/posix/MutexImpl.cpp
@@ -0,0 +1,81 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+
+#include "js/Utility.h"
+
+#include "threading/Mutex.h"
+#include "threading/posix/MutexPlatformData.h"
+
+#define TRY_CALL_PTHREADS(call, msg)            \
+  {                                             \
+    int result = (call);                        \
+    if (result != 0) {                          \
+      errno = result;                           \
+      perror(msg);                              \
+      MOZ_CRASH(msg);                           \
+    }                                           \
+  }
+
+js::detail::MutexImpl::MutexImpl()
+{
+  AutoEnterOOMUnsafeRegion oom;
+  platformData_ = js_new<PlatformData>();
+  if (!platformData_)
+    oom.crash("js::detail::MutexImpl::MutexImpl");
+
+  pthread_mutexattr_t* attrp = nullptr;
+
+#ifdef DEBUG
+  pthread_mutexattr_t attr;
+
+  TRY_CALL_PTHREADS(pthread_mutexattr_init(&attr),
+                    "js::detail::MutexImpl::MutexImpl: pthread_mutexattr_init failed");
+
+  TRY_CALL_PTHREADS(pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK),
+                    "js::detail::MutexImpl::MutexImpl: pthread_mutexattr_settype failed");
+
+  attrp = &attr;
+#endif
+
+  TRY_CALL_PTHREADS(pthread_mutex_init(&platformData()->ptMutex, attrp),
+                    "js::detail::MutexImpl::MutexImpl: pthread_mutex_init failed");
+
+#ifdef DEBUG
+  TRY_CALL_PTHREADS(pthread_mutexattr_destroy(&attr),
+                    "js::detail::MutexImpl::MutexImpl: pthread_mutexattr_destroy failed");
+#endif
+}
+
+js::detail::MutexImpl::~MutexImpl()
+{
+  if (!platformData_)
+    return;
+
+  TRY_CALL_PTHREADS(pthread_mutex_destroy(&platformData()->ptMutex),
+                    "js::detail::MutexImpl::~MutexImpl: pthread_mutex_destroy failed");
+
+  js_delete(platformData());
+}
+
+void
+js::detail::MutexImpl::lock()
+{
+  TRY_CALL_PTHREADS(pthread_mutex_lock(&platformData()->ptMutex),
+                    "js::detail::MutexImpl::lock: pthread_mutex_lock failed");
+}
+
+void
+js::detail::MutexImpl::unlock()
+{
+  TRY_CALL_PTHREADS(pthread_mutex_unlock(&platformData()->ptMutex),
+                    "js::detail::MutexImpl::unlock: pthread_mutex_unlock failed");
+}
+
+#undef TRY_CALL_PTHREADS
diff --git a/js/src/threading/posix/MutexPlatformData.h b/js/src/threading/posix/MutexPlatformData.h
new file mode 100644
index 0000000000..487d89681e
--- /dev/null
+++ b/js/src/threading/posix/MutexPlatformData.h
@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef platform_win_MutexPlatformData_h
+#define platform_win_MutexPlatformData_h
+
+#include <pthread.h>
+
+#include "threading/Mutex.h"
+
+struct js::detail::MutexImpl::PlatformData
+{
+  pthread_mutex_t ptMutex;
+};
+
+#endif // platform_win_MutexPlatformData_h
diff --git a/js/src/threading/posix/Thread.cpp b/js/src/threading/posix/Thread.cpp
new file mode 100644
index 0000000000..2572cc7279
--- /dev/null
+++ b/js/src/threading/posix/Thread.cpp
@@ -0,0 +1,182 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/Assertions.h"
+
+#include <new>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if defined(__APPLE__) && defined(__MACH__)
+#include <dlfcn.h>
+#endif
+
+#if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__OpenBSD__)
+#include <pthread_np.h>
+#endif
+
+#if defined(__linux__)
+#include <sys/prctl.h>
+#endif
+
+#include "threading/Thread.h"
+
+class js::Thread::Id::PlatformData
+{
+  friend class js::Thread;
+  friend js::Thread::Id js::ThisThread::GetId();
+
+  pthread_t ptThread;
+
+  // pthread_t does not have a default initializer, so we have to carry a bool
+  // to tell whether it is safe to compare or not.
+  bool hasThread;
+};
+
+/* static */ js::HashNumber
+js::Thread::Hasher::hash(const Lookup& l)
+{
+  return mozilla::HashBytes(&l.platformData()->ptThread, sizeof(pthread_t));
+}
+
+inline js::Thread::Id::PlatformData*
+js::Thread::Id::platformData()
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}
+
+inline const js::Thread::Id::PlatformData*
+js::Thread::Id::platformData() const
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<const PlatformData*>(platformData_);
+}
+
+js::Thread::Id::Id()
+{
+  platformData()->hasThread = false;
+}
+
+bool
+js::Thread::Id::operator==(const Id& aOther) const
+{
+  const PlatformData& self = *platformData();
+  const PlatformData& other = *aOther.platformData();
+  return (!self.hasThread && !other.hasThread) ||
+         (self.hasThread == other.hasThread &&
+          pthread_equal(self.ptThread, other.ptThread));
+}
+
+js::Thread::Thread(Thread&& aOther)
+{
+  id_ = aOther.id_;
+  aOther.id_ = Id();
+}
+
+js::Thread&
+js::Thread::operator=(Thread&& aOther)
+{
+  MOZ_RELEASE_ASSERT(!joinable());
+  id_ = aOther.id_;
+  aOther.id_ = Id();
+  return *this;
+}
+
+bool
+js::Thread::create(void* (*aMain)(void*), void* aArg)
+{
+  pthread_attr_t attrs;
+  int r = pthread_attr_init(&attrs);
+  MOZ_RELEASE_ASSERT(!r);
+  if (options_.stackSize()) {
+    r = pthread_attr_setstacksize(&attrs, options_.stackSize());
+    MOZ_RELEASE_ASSERT(!r);
+  }
+  r = pthread_create(&id_.platformData()->ptThread, &attrs, aMain, aArg);
+  if (r) {
+    // |pthread_create| may leave id_ in an undefined state.
+    id_ = Id();
+    return false;
+  }
+  id_.platformData()->hasThread = true;
+  return true;
+}
+
+void
+js::Thread::join()
+{
+  MOZ_RELEASE_ASSERT(joinable());
+  int r = pthread_join(id_.platformData()->ptThread, nullptr);
+  MOZ_RELEASE_ASSERT(!r);
+  id_ = Id();
+}
+
+void
+js::Thread::detach()
+{
+  MOZ_RELEASE_ASSERT(joinable());
+  int r = pthread_detach(id_.platformData()->ptThread);
+  MOZ_RELEASE_ASSERT(!r);
+  id_ = Id();
+}
+
+js::Thread::Id
+js::ThisThread::GetId()
+{
+  js::Thread::Id id;
+  id.platformData()->ptThread = pthread_self();
+  id.platformData()->hasThread = true;
+  return id;
+}
+
+void
+js::ThisThread::SetName(const char* name)
+{
+  MOZ_RELEASE_ASSERT(name);
+
+#if (defined(__APPLE__) && defined(__MACH__)) || defined(__linux__)
+  // On linux and OS X the name may not be longer than 16 bytes, including
+  // the null terminator. Truncate the name to 15 characters.
+  char nameBuf[16];
+
+  strncpy(nameBuf, name, sizeof nameBuf - 1);
+  nameBuf[sizeof nameBuf - 1] = '\0';
+  name = nameBuf;
+#endif
+
+  int rv;
+#ifdef XP_DARWIN
+  rv = pthread_setname_np(name);
+#elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__OpenBSD__)
+  pthread_set_name_np(pthread_self(), name);
+  rv = 0;
+#elif defined(__NetBSD__)
+  rv = pthread_setname_np(pthread_self(), "%s", (void*)name);
+#else
+  rv = pthread_setname_np(pthread_self(), name);
+#endif
+  MOZ_RELEASE_ASSERT(!rv);
+}
+
+void
+js::ThisThread::GetName(char* nameBuffer, size_t len)
+{
+  MOZ_RELEASE_ASSERT(len >= 16);
+
+  int rv = -1;
+#ifdef HAVE_PTHREAD_GETNAME_NP
+  rv = pthread_getname_np(pthread_self(), nameBuffer, len);
+#elif defined(__linux__)
+  rv = prctl(PR_GET_NAME, reinterpret_cast<unsigned long>(nameBuffer));
+#endif
+
+  if (rv)
+    nameBuffer[0] = '\0';
+}
diff --git a/js/src/threading/windows/ConditionVariable.cpp b/js/src/threading/windows/ConditionVariable.cpp
new file mode 100644
index 0000000000..868c351416
--- /dev/null
+++ b/js/src/threading/windows/ConditionVariable.cpp
@@ -0,0 +1,418 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/Assertions.h"
+
+#include <float.h>
+#include <intrin.h>
+#include <stdlib.h>
+#include <windows.h>
+
+#include "threading/ConditionVariable.h"
+#include "threading/Mutex.h"
+#include "threading/windows/MutexPlatformData.h"
+
+// Some versions of the Windows SDK have a bug where some interlocked functions
+// are not redefined as compiler intrinsics. Fix that for the interlocked
+// functions that are used in this file.
+#if defined(_MSC_VER) && !defined(InterlockedExchangeAdd)
+#define InterlockedExchangeAdd(addend, value)                                  \
+  _InterlockedExchangeAdd((volatile long*)(addend), (long)(value))
+#endif
+
+#if defined(_MSC_VER) && !defined(InterlockedIncrement)
+#define InterlockedIncrement(addend)                                           \
+  _InterlockedIncrement((volatile long*)(addend))
+#endif
+
+// Windows XP and Server 2003 don't support condition variables natively. The
+// NativeImports class is responsible for detecting native support and
+// retrieving the appropriate function pointers. It gets instantiated once,
+// using a static initializer.
+class ConditionVariableNativeImports
+{
+public:
+  ConditionVariableNativeImports() {
+    HMODULE kernel32_dll = GetModuleHandle("kernel32.dll");
+    MOZ_RELEASE_ASSERT(kernel32_dll != NULL);
+
+#define LOAD_SYMBOL(symbol) loadSymbol(kernel32_dll, #symbol, symbol)
+    supported_ = LOAD_SYMBOL(InitializeConditionVariable) &&
+                 LOAD_SYMBOL(WakeConditionVariable) &&
+                 LOAD_SYMBOL(WakeAllConditionVariable) &&
+                 LOAD_SYMBOL(SleepConditionVariableCS);
+#undef LOAD_SYMBOL
+  }
+
+  inline bool supported() const {
+    return supported_;
+  }
+
+  void(WINAPI* InitializeConditionVariable)(CONDITION_VARIABLE* ConditionVariable);
+  void(WINAPI* WakeAllConditionVariable)(PCONDITION_VARIABLE ConditionVariable);
+  void(WINAPI* WakeConditionVariable)(CONDITION_VARIABLE* ConditionVariable);
+  BOOL(WINAPI* SleepConditionVariableCS)(CONDITION_VARIABLE* ConditionVariable,
+                                         CRITICAL_SECTION* CriticalSection,
+                                         DWORD dwMilliseconds);
+
+private:
+  template <typename T>
+  inline bool loadSymbol(HMODULE module, const char* name, T& fn) {
+    FARPROC ptr = GetProcAddress(module, name);
+    if (!ptr)
+      return false;
+
+    fn = reinterpret_cast<T>(ptr);
+    return true;
+  }
+
+  bool supported_;
+};
+
+static ConditionVariableNativeImports sNativeImports;
+
+// Wrapper for native condition variable APIs.
+struct ConditionVariableNative
+{
+  inline void initialize() {
+    sNativeImports.InitializeConditionVariable(&cv_);
+  }
+
+  inline void destroy() {
+    // Native condition variables don't require cleanup.
+  }
+
+  inline void notify_one() { sNativeImports.WakeConditionVariable(&cv_); }
+
+  inline void notify_all() { sNativeImports.WakeAllConditionVariable(&cv_); }
+
+  inline bool wait(CRITICAL_SECTION* cs, DWORD msec) {
+    return sNativeImports.SleepConditionVariableCS(&cv_, cs, msec);
+  }
+
+private:
+  CONDITION_VARIABLE cv_;
+};
+
+// Fallback condition variable support for Windows XP and Server 2003. Given the
+// difficulty of testing on these antiquated platforms and their rapidly
+// diminishing market share, this implementation trades performance for
+// predictable behavior.
+struct ConditionVariableFallback
+{
+  static const uint32_t WAKEUP_MODE_NONE = 0;
+  static const uint32_t WAKEUP_MODE_ONE = 0x40000000;
+  static const uint32_t WAKEUP_MODE_ALL = 0x80000000;
+
+  static const uint32_t WAKEUP_MODE_MASK = WAKEUP_MODE_ONE | WAKEUP_MODE_ALL;
+  static const uint32_t SLEEPERS_COUNT_MASK = ~WAKEUP_MODE_MASK;
+
+  void initialize()
+  {
+    // Initialize the state variable to 0 sleepers, no wakeup.
+    sleepersCountAndWakeupMode_ = 0 | WAKEUP_MODE_NONE;
+
+    // Create a semaphore that prevents threads from entering sleep,
+    // or waking other threads while a wakeup is ongoing.
+    sleepWakeupSemaphore_ = CreateSemaphoreW(NULL, 1, 1, NULL);
+    MOZ_RELEASE_ASSERT(sleepWakeupSemaphore_);
+
+    // Use an auto-reset event for waking up a single sleeper.
+    wakeOneEvent_ = CreateEventW(NULL, FALSE, FALSE, NULL);
+    MOZ_RELEASE_ASSERT(wakeOneEvent_);
+
+    // Use a manual-reset event for waking up all sleepers.
+    wakeAllEvent_ = CreateEventW(NULL, TRUE, FALSE, NULL);
+    MOZ_RELEASE_ASSERT(wakeAllEvent_);
+  }
+
+  void destroy()
+  {
+    BOOL r;
+
+    MOZ_RELEASE_ASSERT(sleepersCountAndWakeupMode_ == (0 | WAKEUP_MODE_NONE));
+
+    r = CloseHandle(sleepWakeupSemaphore_);
+    MOZ_RELEASE_ASSERT(r);
+
+    r = CloseHandle(wakeOneEvent_);
+    MOZ_RELEASE_ASSERT(r);
+
+    r = CloseHandle(wakeAllEvent_);
+    MOZ_RELEASE_ASSERT(r);
+  }
+
+private:
+  void wakeup(uint32_t wakeupMode, HANDLE wakeEvent)
+  {
+    // Ensure that only one thread at a time can wake up others.
+    BOOL result = WaitForSingleObject(sleepWakeupSemaphore_, INFINITE);
+    MOZ_RELEASE_ASSERT(result == WAIT_OBJECT_0);
+
+    // Atomically set the wakeup mode and retrieve the number of sleepers.
+    uint32_t wcwm = InterlockedExchangeAdd(&sleepersCountAndWakeupMode_,
+                                           wakeupMode);
+    uint32_t sleepersCount = wcwm & SLEEPERS_COUNT_MASK;
+    MOZ_RELEASE_ASSERT((wcwm & WAKEUP_MODE_MASK) == WAKEUP_MODE_NONE);
+
+    if (sleepersCount > 0) {
+      // If there are any sleepers, set the wake event. The (last) woken
+      // up thread is responsible for releasing the semaphore.
+      BOOL success = SetEvent(wakeEvent);
+      MOZ_RELEASE_ASSERT(success);
+
+    } else {
+      // If there are no sleepers, set the wakeup mode back to 'none'
+      // and release the semaphore ourselves.
+      sleepersCountAndWakeupMode_ = 0 | WAKEUP_MODE_NONE;
+
+      BOOL success = ReleaseSemaphore(sleepWakeupSemaphore_, 1, NULL);
+      MOZ_RELEASE_ASSERT(success);
+    }
+  }
+
+public:
+  void notify_one() { wakeup(WAKEUP_MODE_ONE, wakeOneEvent_); }
+
+  void notify_all() { wakeup(WAKEUP_MODE_ALL, wakeAllEvent_); }
+
+  bool wait(CRITICAL_SECTION* userLock, DWORD msec)
+  {
+    // Make sure that we can't enter sleep when there are other threads
+    // that still need to wake up on either of the wake events being set.
+    DWORD result = WaitForSingleObject(sleepWakeupSemaphore_, INFINITE);
+    MOZ_RELEASE_ASSERT(result == WAIT_OBJECT_0);
+
+    // Register ourselves as a sleeper. Use an atomic operation, because
+    // if another thread times out at the same time, it will decrement the
+    // sleepers count without acquiring the semaphore.
+    uint32_t wcwm = InterlockedIncrement(&sleepersCountAndWakeupMode_);
+    MOZ_RELEASE_ASSERT((wcwm & WAKEUP_MODE_MASK) == WAKEUP_MODE_NONE);
+
+    // Now that that this thread has been enlisted as a sleeper, it is safe
+    // again for other threads to do a wakeup.
+    BOOL success = ReleaseSemaphore(sleepWakeupSemaphore_, 1, NULL);
+    MOZ_RELEASE_ASSERT(success);
+
+    // Release the caller's mutex.
+    LeaveCriticalSection(userLock);
+
+    // Wait for either event to become signaled, which happens when
+    // notify_one() or notify_all() is called, or for a timeout.
+    HANDLE handles[2] = { wakeOneEvent_, wakeAllEvent_ };
+    DWORD waitResult = WaitForMultipleObjects(2, handles, FALSE, msec);
+    MOZ_RELEASE_ASSERT(waitResult == WAIT_OBJECT_0 ||
+                       waitResult == WAIT_OBJECT_0 + 1 ||
+                       (waitResult == WAIT_TIMEOUT && msec != INFINITE));
+
+    // Atomically decrease the sleepers count and retrieve the wakeup mode
+    // and new sleepers count.
+    // If the wait returned because wakeOneEvent_ was set, we are certain
+    // that the wakeup mode will be WAKEUP_MODE_ONE. In that case,
+    // atomically reset the wakeup mode to 'none', because if another
+    // thread's sleep times out at same time and it finds that it was the
+    // last sleeper, it decides whether or not to reset the wakeOneEvent_
+    // based on the current wakeup mode.
+    uint32_t sub;
+    if (waitResult == WAIT_OBJECT_0)
+      sub = 1 | WAKEUP_MODE_ONE;
+    else
+      sub = 1;
+    // Note that InterlockedExchangeAdd returns the old value, but it's
+    // easier to work with the new value.
+    wcwm = InterlockedExchangeAdd(&sleepersCountAndWakeupMode_, -sub) - sub;
+
+    uint32_t wakeupMode = wcwm & WAKEUP_MODE_MASK;
+    uint32_t sleepersCount = wcwm & SLEEPERS_COUNT_MASK;
+
+    bool releaseSleepWakeupSemaphore = false;
+
+    if (waitResult == WAIT_OBJECT_0) {
+      // The wake-one event is an auto-reset event so if we're woken by
+      // it, it should already have been reset. We also already removed
+      // the WAKEUP_MODE_ONE bit so the wakeup mode should now be 'none'
+      // again.
+      MOZ_RELEASE_ASSERT(wakeupMode == WAKEUP_MODE_NONE);
+
+      // The signaling thread has acquired the enter-wakeup semaphore and
+      // expects the woken (this) thread to release it again.
+      releaseSleepWakeupSemaphore = true;
+
+    } else if (waitResult == WAIT_TIMEOUT && wakeupMode == WAKEUP_MODE_ONE &&
+               sleepersCount == 0) {
+      // In theory a race condition is possible where the last sleeper
+      // times out right at the moment that another thread signals it.
+      // If that just happened we now have a dangling signal event and
+      // mode, but no threads to be woken up by it, and we need to clean
+      // that up.
+      BOOL success = ResetEvent(wakeOneEvent_);
+      MOZ_RELEASE_ASSERT(success);
+
+      // This is safe - we are certain there are no other sleepers that
+      // could wake up right now, and the semaphore ensures that no
+      // non-sleeping threads are messing with
+      // sleepersCountAndWakeupMode_.
+      sleepersCountAndWakeupMode_ = 0 | WAKEUP_MODE_NONE;
+
+      // The signaling thread has acquired the sleep-wakeup semaphore and
+      // expects the woken thread to release it. But since there are no
+      // sleeping threads left this thread will do it instead.
+      releaseSleepWakeupSemaphore = true;
+
+    } else if (wakeupMode == WAKEUP_MODE_ALL && sleepersCount == 0) {
+      // If this was the last thread waking up in response to a
+      // notify_all, clear the wakeup mode and reset the wake-all event.
+      // A race condition similar to the case described above could
+      // occur, so waitResult could be WAIT_TIMEOUT, but that doesn't
+      // matter for the actions that need to be taken.
+      MOZ_RELEASE_ASSERT(waitResult = WAIT_OBJECT_0 + 1 ||
+                         waitResult == WAIT_TIMEOUT);
+
+      BOOL success = ResetEvent(wakeAllEvent_);
+      MOZ_RELEASE_ASSERT(success);
+
+      sleepersCountAndWakeupMode_ = 0 | WAKEUP_MODE_NONE;
+
+      // The broadcasting thread has acquired the enter-wakeup semaphore
+      // and expects the last thread that wakes up to release it.
+      releaseSleepWakeupSemaphore = true;
+
+    } else if ((waitResult == WAIT_TIMEOUT && msec != INFINITE) ||
+               (waitResult == WAIT_OBJECT_0 + 1 &&
+                wakeupMode == WAKEUP_MODE_ALL)) {
+      // Either:
+      //   * The wait timed out but found no active notify_one or notify_all
+      //     the moment it decreased the wait count.
+      //   * A notify_all woke up this thread but there are more threads
+      //     that need to be woken up by the wake-all event.
+      // These are ordinary conditions in which we don't have to do
+      // anything.
+
+    } else {
+      MOZ_CRASH("invalid wakeup condition");
+    }
+
+    // Release the enter-wakeup semaphore if the wakeup condition requires
+    // us to do it.
+    if (releaseSleepWakeupSemaphore) {
+      BOOL success = ReleaseSemaphore(sleepWakeupSemaphore_, 1, NULL);
+      MOZ_RELEASE_ASSERT(success);
+    }
+
+    // Reacquire the user mutex.
+    EnterCriticalSection(userLock);
+
+    // Return true if woken up, false when timed out.
+    if (waitResult == WAIT_TIMEOUT) {
+      SetLastError(ERROR_TIMEOUT);
+      return false;
+    }
+    return true;
+  }
+
+private:
+  uint32_t sleepersCountAndWakeupMode_;
+  HANDLE sleepWakeupSemaphore_;
+  HANDLE wakeOneEvent_;
+  HANDLE wakeAllEvent_;
+};
+
+struct js::ConditionVariable::PlatformData
+{
+  union
+  {
+    ConditionVariableNative native;
+    ConditionVariableFallback fallback;
+  };
+};
+
+js::ConditionVariable::ConditionVariable()
+{
+  if (sNativeImports.supported())
+    platformData()->native.initialize();
+  else
+    platformData()->fallback.initialize();
+}
+
+void
+js::ConditionVariable::notify_one()
+{
+  if (sNativeImports.supported())
+    platformData()->native.notify_one();
+  else
+    platformData()->fallback.notify_one();
+}
+
+void
+js::ConditionVariable::notify_all()
+{
+  if (sNativeImports.supported())
+    platformData()->native.notify_all();
+  else
+    platformData()->fallback.notify_all();
+}
+
+void
+js::ConditionVariable::wait(UniqueLock<Mutex>& lock)
+{
+  CRITICAL_SECTION* cs = &lock.lock.platformData()->criticalSection;
+  bool r;
+  if (sNativeImports.supported())
+    r = platformData()->native.wait(cs, INFINITE);
+  else
+    r = platformData()->fallback.wait(cs, INFINITE);
+  MOZ_RELEASE_ASSERT(r);
+}
+
+js::CVStatus
+js::ConditionVariable::wait_until(UniqueLock<Mutex>& lock,
+                                  const mozilla::TimeStamp& abs_time)
+{
+  return wait_for(lock, abs_time - mozilla::TimeStamp::Now());
+}
+
+js::CVStatus
+js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
+                                const mozilla::TimeDuration& rel_time)
+{
+  CRITICAL_SECTION* cs = &lock.lock.platformData()->criticalSection;
+
+  // Note that DWORD is unsigned, so we have to be careful to clamp at 0.
+  // If rel_time is Forever, then ToMilliseconds is +inf, which evaluates as
+  // greater than UINT32_MAX, resulting in the correct INFINITE wait.
+  double msecd = rel_time.ToMilliseconds();
+  DWORD msec = msecd < 0.0
+               ? 0
+               : msecd > UINT32_MAX
+                 ? INFINITE
+                 : static_cast<DWORD>(msecd);
+
+  BOOL r;
+  if (sNativeImports.supported())
+    r = platformData()->native.wait(cs, msec);
+  else
+    r = platformData()->fallback.wait(cs, msec);
+  if (r)
+    return CVStatus::NoTimeout;
+  MOZ_RELEASE_ASSERT(GetLastError() == ERROR_TIMEOUT);
+  return CVStatus::Timeout;
+}
+
+js::ConditionVariable::~ConditionVariable()
+{
+  if (sNativeImports.supported())
+    platformData()->native.destroy();
+  else
+    platformData()->fallback.destroy();
+}
+
+inline js::ConditionVariable::PlatformData*
+js::ConditionVariable::platformData()
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}
diff --git a/js/src/threading/windows/MutexImpl.cpp b/js/src/threading/windows/MutexImpl.cpp
new file mode 100644
index 0000000000..385d1c8dec
--- /dev/null
+++ b/js/src/threading/windows/MutexImpl.cpp
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/DebugOnly.h"
+
+#include "jswin.h"
+
+#include "js/Utility.h"
+
+#include "threading/Mutex.h"
+#include "threading/windows/MutexPlatformData.h"
+
+namespace {
+
+// We build with a toolkit that supports WinXP, so we have to probe
+// for modern features at runtime. This is necessary because Vista and
+// later automatically allocate and subsequently leak a debug info
+// object for each critical section that we allocate unless we tell it
+// not to. In order to tell it not to, we need the extra flags field
+// provided by the Ex version of InitializeCriticalSection.
+struct MutexNativeImports
+{
+  using InitializeCriticalSectionExT = BOOL (WINAPI*)(CRITICAL_SECTION*, DWORD, DWORD);
+  InitializeCriticalSectionExT InitializeCriticalSectionEx;
+
+  MutexNativeImports() {
+    HMODULE kernel32_dll = GetModuleHandle("kernel32.dll");
+    MOZ_RELEASE_ASSERT(kernel32_dll != NULL);
+    InitializeCriticalSectionEx = reinterpret_cast<InitializeCriticalSectionExT>(
+      GetProcAddress(kernel32_dll, "InitializeCriticalSectionEx"));
+  }
+
+  bool hasInitializeCriticalSectionEx() const {
+    return InitializeCriticalSectionEx;
+  }
+};
+
+static MutexNativeImports NativeImports;
+
+} // (anonymous namespace)
+
+js::detail::MutexImpl::MutexImpl()
+{
+  AutoEnterOOMUnsafeRegion oom;
+  platformData_ = js_new<PlatformData>();
+  if (!platformData_)
+    oom.crash("js::Mutex::Mutex");
+
+  // This number was adopted from NSPR.
+  const static DWORD LockSpinCount = 1500;
+  BOOL r;
+  if (NativeImports.hasInitializeCriticalSectionEx()) {
+    r = NativeImports.InitializeCriticalSectionEx(&platformData()->criticalSection,
+                                                  LockSpinCount,
+                                                  CRITICAL_SECTION_NO_DEBUG_INFO);
+  } else {
+    r = InitializeCriticalSectionAndSpinCount(&platformData()->criticalSection,
+                                              LockSpinCount);
+  }
+  MOZ_RELEASE_ASSERT(r);
+}
+
+js::detail::MutexImpl::~MutexImpl()
+{
+  if (!platformData_)
+    return;
+
+  DeleteCriticalSection(&platformData()->criticalSection);
+  js_delete(platformData());
+}
+
+void
+js::detail::MutexImpl::lock()
+{
+  EnterCriticalSection(&platformData()->criticalSection);
+}
+
+void
+js::detail::MutexImpl::unlock()
+{
+  LeaveCriticalSection(&platformData()->criticalSection);
+}
diff --git a/js/src/threading/windows/MutexPlatformData.h b/js/src/threading/windows/MutexPlatformData.h
new file mode 100644
index 0000000000..fbe7fc80d8
--- /dev/null
+++ b/js/src/threading/windows/MutexPlatformData.h
@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef platform_win_MutexPlatformData_h
+#define platform_win_MutexPlatformData_h
+
+#include "jswin.h"
+
+#include "threading/Mutex.h"
+
+struct js::detail::MutexImpl::PlatformData
+{
+  CRITICAL_SECTION criticalSection;
+};
+
+#endif // platform_win_MutexPlatformData_h
diff --git a/js/src/threading/windows/Thread.cpp b/js/src/threading/windows/Thread.cpp
new file mode 100644
index 0000000000..29e8b16a11
--- /dev/null
+++ b/js/src/threading/windows/Thread.cpp
@@ -0,0 +1,164 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <assert.h>
+#include <new.h>
+#include <process.h>
+
+#include <windows.h>
+
+#include "threading/Thread.h"
+
+class js::Thread::Id::PlatformData
+{
+  friend class js::Thread;
+  friend js::Thread::Id js::ThisThread::GetId();
+
+  HANDLE handle;
+  unsigned id;
+};
+
+/* static */ js::HashNumber
+js::Thread::Hasher::hash(const Lookup& l)
+{
+  return mozilla::HashBytes(l.platformData_, sizeof(l.platformData_));
+}
+
+inline js::Thread::Id::PlatformData*
+js::Thread::Id::platformData()
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}
+
+inline const js::Thread::Id::PlatformData*
+js::Thread::Id::platformData() const
+{
+  static_assert(sizeof platformData_ >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<const PlatformData*>(platformData_);
+}
+
+js::Thread::Id::Id()
+{
+  platformData()->handle = nullptr;
+  platformData()->id = 0;
+}
+
+bool
+js::Thread::Id::operator==(const Id& aOther) const
+{
+  return platformData()->id == aOther.platformData()->id;
+}
+
+js::Thread::Thread(Thread&& aOther)
+{
+  id_ = aOther.id_;
+  aOther.id_ = Id();
+}
+
+js::Thread&
+js::Thread::operator=(Thread&& aOther)
+{
+  MOZ_RELEASE_ASSERT(!joinable());
+  id_ = aOther.id_;
+  aOther.id_ = Id();
+  return *this;
+}
+
+bool
+js::Thread::create(unsigned int (__stdcall* aMain)(void*), void* aArg)
+{
+  // Use _beginthreadex and not CreateThread, because threads that are
+  // created with the latter leak a small amount of memory when they use
+  // certain msvcrt functions and then exit.
+  uintptr_t handle = _beginthreadex(nullptr, options_.stackSize(),
+                                    aMain, aArg,
+                                    STACK_SIZE_PARAM_IS_A_RESERVATION,
+                                    &id_.platformData()->id);
+  if (!handle) {
+    // The documentation does not say what state the thread id has if the method
+    // fails, so assume that it is undefined and reset it manually.
+    id_ = Id();
+    return false;
+  }
+  id_.platformData()->handle = reinterpret_cast<HANDLE>(handle);
+  return true;
+}
+
+void
+js::Thread::join()
+{
+  MOZ_RELEASE_ASSERT(joinable());
+  DWORD r = WaitForSingleObject(id_.platformData()->handle, INFINITE);
+  MOZ_RELEASE_ASSERT(r == WAIT_OBJECT_0);
+  BOOL success = CloseHandle(id_.platformData()->handle);
+  MOZ_RELEASE_ASSERT(success);
+  id_ = Id();
+}
+
+void
+js::Thread::detach()
+{
+  MOZ_RELEASE_ASSERT(joinable());
+  BOOL success = CloseHandle(id_.platformData()->handle);
+  MOZ_RELEASE_ASSERT(success);
+  id_ = Id();
+}
+
+js::Thread::Id
+js::ThisThread::GetId()
+{
+  js::Thread::Id id;
+  id.platformData()->handle = GetCurrentThread();
+  id.platformData()->id = GetCurrentThreadId();
+  MOZ_RELEASE_ASSERT(id != js::Thread::Id());
+  return id;
+}
+
+void
+js::ThisThread::SetName(const char* name)
+{
+  MOZ_RELEASE_ASSERT(name);
+
+#ifdef _MSC_VER
+  // Setting the thread name requires compiler support for structured
+  // exceptions, so this only works when compiled with MSVC.
+  static const DWORD THREAD_NAME_EXCEPTION = 0x406D1388;
+  static const DWORD THREAD_NAME_INFO_TYPE = 0x1000;
+
+#pragma pack(push, 8)
+  struct THREADNAME_INFO
+  {
+    DWORD dwType;
+    LPCSTR szName;
+    DWORD dwThreadID;
+    DWORD dwFlags;
+  };
+#pragma pack(pop)
+
+  THREADNAME_INFO info;
+  info.dwType = THREAD_NAME_INFO_TYPE;
+  info.szName = name;
+  info.dwThreadID = GetCurrentThreadId();
+  info.dwFlags = 0;
+
+  __try {
+    RaiseException(THREAD_NAME_EXCEPTION, 0, sizeof(info) / sizeof(ULONG_PTR),
+                   (ULONG_PTR*)&info);
+  } __except (EXCEPTION_EXECUTE_HANDLER) {
+    // Do nothing.
+  }
+#endif
+}
+
+void
+js::ThisThread::GetName(char* nameBuffer, size_t len)
+{
+  MOZ_RELEASE_ASSERT(len > 0);
+  *nameBuffer = '\0';
+}