Merge pull request 'Update IPC locking code.' (#2004) from athenian200/UXP:ipc-locking-update into master

Reviewed-on: https://repo.palemoon.org/MoonchildProductions/UXP/pulls/2004

9 files changed, 190 insertions, 645 deletions

diff --git a/ipc/chromium/moz.build b/ipc/chromium/moz.build
index 4050307fe9..e79c7f3753 100644
--- a/ipc/chromium/moz.build
+++ b/ipc/chromium/moz.build
@@ -12,7 +12,6 @@ UNIFIED_SOURCES += [
     'src/base/file_path.cc',
     'src/base/file_util.cc',
     'src/base/histogram.cc',
-    'src/base/lock.cc',
     'src/base/logging.cc',
     'src/base/message_loop.cc',
     'src/base/message_pump_default.cc',
diff --git a/ipc/chromium/src/base/condition_variable.h b/ipc/chromium/src/base/condition_variable.h
index 63610e0e3b..f274c8eabe 100644
--- a/ipc/chromium/src/base/condition_variable.h
+++ b/ipc/chromium/src/base/condition_variable.h
@@ -1,5 +1,4 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -66,7 +65,17 @@
 #ifndef BASE_CONDITION_VARIABLE_H_
 #define BASE_CONDITION_VARIABLE_H_
 
+#include "base/basictypes.h"
 #include "base/lock.h"
+#include "build/build_config.h"
+
+#if defined(OS_POSIX)
+#include <pthread.h>
+#endif
+
+#if defined(OS_WIN)
+#include <windows.h>
+#endif
 
 namespace base {
   class TimeDelta;
@@ -80,11 +89,13 @@ class ConditionVariable {
   ~ConditionVariable();
 
   // Wait() releases the caller's critical section atomically as it starts to
-  // sleep, and the reacquires it when it is signaled.
+  // sleep, and the reacquires it when it is signaled. The wait functions are
+  // susceptible to spurious wakeups. (See usage note 1 for more details.)
   void Wait();
   void TimedWait(const base::TimeDelta& max_time);
 
-  // Broadcast() revives all waiting threads.
+  // Broadcast() revives all waiting threads. (See usage note 2 for more
+  // details.)
   void Broadcast();
   // Signal() revives one waiting thread.
   void Signal();
@@ -92,81 +103,11 @@ class ConditionVariable {
  private:
 
 #if defined(OS_WIN)
-
-  // Define Event class that is used to form circularly linked lists.
-  // The list container is an element with NULL as its handle_ value.
-  // The actual list elements have a non-zero handle_ value.
-  // All calls to methods MUST be done under protection of a lock so that links
-  // can be validated.  Without the lock, some links might asynchronously
-  // change, and the assertions would fail (as would list change operations).
-  class Event {
-   public:
-    // Default constructor with no arguments creates a list container.
-    Event();
-    ~Event();
-
-    // InitListElement transitions an instance from a container, to an element.
-    void InitListElement();
-
-    // Methods for use on lists.
-    bool IsEmpty() const;
-    void PushBack(Event* other);
-    Event* PopFront();
-    Event* PopBack();
-
-    // Methods for use on list elements.
-    // Accessor method.
-    HANDLE handle() const;
-    // Pull an element from a list (if it's in one).
-    Event* Extract();
-
-    // Method for use on a list element or on a list.
-    bool IsSingleton() const;
-
-   private:
-    // Provide pre/post conditions to validate correct manipulations.
-    bool ValidateAsDistinct(Event* other) const;
-    bool ValidateAsItem() const;
-    bool ValidateAsList() const;
-    bool ValidateLinks() const;
-
-    HANDLE handle_;
-    Event* next_;
-    Event* prev_;
-    DISALLOW_COPY_AND_ASSIGN(Event);
-  };
-
-  // Note that RUNNING is an unlikely number to have in RAM by accident.
-  // This helps with defensive destructor coding in the face of user error.
-  enum RunState { SHUTDOWN = 0, RUNNING = 64213 };
-
-  // Internal implementation methods supporting Wait().
-  Event* GetEventForWaiting();
-  void RecycleEvent(Event* used_event);
-
-  RunState run_state_;
-
-  // Private critical section for access to member data.
-  Lock internal_lock_;
-
-  // Lock that is acquired before calling Wait().
-  Lock& user_lock_;
-
-  // Events that threads are blocked on.
-  Event waiting_list_;
-
-  // Free list for old events.
-  Event recycling_list_;
-  int recycling_list_size_;
-
-  // The number of allocated, but not yet deleted events.
-  int allocation_counter_;
-
+  CONDITION_VARIABLE cv_;
+  SRWLOCK* const srwlock_;
 #elif defined(OS_POSIX)
-
   pthread_cond_t condition_;
   pthread_mutex_t* user_mutex_;
-
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
diff --git a/ipc/chromium/src/base/condition_variable_posix.cc b/ipc/chromium/src/base/condition_variable_posix.cc
index 4a8024c2bc..8b689f5e5d 100644
--- a/ipc/chromium/src/base/condition_variable_posix.cc
+++ b/ipc/chromium/src/base/condition_variable_posix.cc
@@ -1,23 +1,19 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/condition_variable.h"
 
 #include <errno.h>
+#include <stdint.h>
 #include <sys/time.h>
 
 #include "base/lock.h"
-#include "base/lock_impl.h"
-#include "base/logging.h"
 #include "base/time.h"
-
-using base::Time;
-using base::TimeDelta;
+#include "build/build_config.h"
 
 ConditionVariable::ConditionVariable(Lock* user_lock)
-    : user_mutex_(user_lock->lock_impl()->os_lock()) {
+    : user_mutex_(user_lock->lock_.native_handle()) {
   int rv = 0;
 #if !defined(OS_MACOSX)
   pthread_condattr_t attrs;
@@ -33,52 +29,66 @@ ConditionVariable::ConditionVariable(Lock* user_lock)
 }
 
 ConditionVariable::~ConditionVariable() {
+#if defined(OS_MACOSX)
+  // This hack is necessary to avoid a fatal pthreads subsystem bug in the
+  // Darwin kernel. http://crbug.com/517681.
+  {
+    Lock lock;
+    AutoLock l(lock);
+    struct timespec ts;
+    ts.tv_sec = 0;
+    ts.tv_nsec = 1;
+    pthread_cond_timedwait_relative_np(&condition_, lock.lock_.native_handle(),
+                                       &ts);
+  }
+#endif
   int rv = pthread_cond_destroy(&condition_);
-  DCHECK(rv == 0);
+  DCHECK_EQ(0, rv);
 }
 
 void ConditionVariable::Wait() {
   int rv = pthread_cond_wait(&condition_, user_mutex_);
-  DCHECK(rv == 0);
+  DCHECK_EQ(0, rv);
 }
 
-void ConditionVariable::TimedWait(const TimeDelta& max_time) {
+void ConditionVariable::TimedWait(const base::TimeDelta& max_time) {
   int64_t usecs = max_time.InMicroseconds();
-
   struct timespec relative_time;
-  relative_time.tv_sec = usecs / Time::kMicrosecondsPerSecond;
+  relative_time.tv_sec = usecs / base::Time::kMicrosecondsPerSecond;
   relative_time.tv_nsec =
-      (usecs % Time::kMicrosecondsPerSecond) * Time::kNanosecondsPerMicrosecond;
+      (usecs % base::Time::kMicrosecondsPerSecond) * base::Time::kNanosecondsPerMicrosecond;
 
 #if defined(OS_MACOSX)
   int rv = pthread_cond_timedwait_relative_np(
       &condition_, user_mutex_, &relative_time);
 #else
   // The timeout argument to pthread_cond_timedwait is in absolute time.
+  struct timespec absolute_time;
   struct timespec now;
   clock_gettime(CLOCK_MONOTONIC, &now);
-
-  struct timespec absolute_time;
   absolute_time.tv_sec = now.tv_sec;
   absolute_time.tv_nsec = now.tv_nsec;
   absolute_time.tv_sec += relative_time.tv_sec;
   absolute_time.tv_nsec += relative_time.tv_nsec;
-  absolute_time.tv_sec += absolute_time.tv_nsec / Time::kNanosecondsPerSecond;
-  absolute_time.tv_nsec %= Time::kNanosecondsPerSecond;
+  absolute_time.tv_sec += absolute_time.tv_nsec / base::Time::kNanosecondsPerSecond;
+  absolute_time.tv_nsec %= base::Time::kNanosecondsPerSecond;
   DCHECK_GE(absolute_time.tv_sec, now.tv_sec);  // Overflow paranoia
 
   int rv = pthread_cond_timedwait(&condition_, user_mutex_, &absolute_time);
 #endif  // OS_MACOSX
 
+
+  // On failure, we only expect the CV to timeout. Any other error value means
+  // that we've unexpectedly woken up.
   DCHECK(rv == 0 || rv == ETIMEDOUT);
 }
 
 void ConditionVariable::Broadcast() {
   int rv = pthread_cond_broadcast(&condition_);
-  DCHECK(rv == 0);
+  DCHECK_EQ(0, rv);
 }
 
 void ConditionVariable::Signal() {
   int rv = pthread_cond_signal(&condition_);
-  DCHECK(rv == 0);
+  DCHECK_EQ(0, rv);
 }
diff --git a/ipc/chromium/src/base/condition_variable_win.cc b/ipc/chromium/src/base/condition_variable_win.cc
index 8737781375..468fe8951d 100644
--- a/ipc/chromium/src/base/condition_variable_win.cc
+++ b/ipc/chromium/src/base/condition_variable_win.cc
@@ -1,447 +1,47 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/condition_variable.h"
 
-#include <stack>
-
 #include "base/lock.h"
 #include "base/logging.h"
 #include "base/time.h"
 
-using base::TimeDelta;
-
 ConditionVariable::ConditionVariable(Lock* user_lock)
-  : user_lock_(*user_lock),
-    run_state_(RUNNING),
-    allocation_counter_(0),
-    recycling_list_size_(0) {
+    : srwlock_(user_lock->lock_.native_handle())
+{
   DCHECK(user_lock);
+  InitializeConditionVariable(&cv_);
 }
 
-ConditionVariable::~ConditionVariable() {
-  AutoLock auto_lock(internal_lock_);
-  run_state_ = SHUTDOWN;  // Prevent any more waiting.
 
-  DCHECK_EQ(recycling_list_size_, allocation_counter_);
-  if (recycling_list_size_ != allocation_counter_) {  // Rare shutdown problem.
-    // There are threads of execution still in this->TimedWait() and yet the
-    // caller has instigated the destruction of this instance :-/.
-    // A common reason for such "overly hasty" destruction is that the caller
-    // was not willing to wait for all the threads to terminate.  Such hasty
-    // actions are a violation of our usage contract, but we'll give the
-    // waiting thread(s) one last chance to exit gracefully (prior to our
-    // destruction).
-    // Note: waiting_list_ *might* be empty, but recycling is still pending.
-    AutoUnlock auto_unlock(internal_lock_);
-    Broadcast();  // Make sure all waiting threads have been signaled.
-    Sleep(10);  // Give threads a chance to grab internal_lock_.
-    // All contained threads should be blocked on user_lock_ by now :-).
-  }  // Reacquire internal_lock_.
-
-  DCHECK_EQ(recycling_list_size_, allocation_counter_);
-}
+ConditionVariable::~ConditionVariable() = default;
 
 void ConditionVariable::Wait() {
   // Default to "wait forever" timing, which means have to get a Signal()
   // or Broadcast() to come out of this wait state.
-  TimedWait(TimeDelta::FromMilliseconds(INFINITE));
+  TimedWait(base::TimeDelta::FromMilliseconds(INFINITE));
 }
 
-void ConditionVariable::TimedWait(const TimeDelta& max_time) {
-  Event* waiting_event;
-  HANDLE handle;
-  {
-    AutoLock auto_lock(internal_lock_);
-    if (RUNNING != run_state_) return;  // Destruction in progress.
-    waiting_event = GetEventForWaiting();
-    handle = waiting_event->handle();
-    DCHECK(handle);
-  }  // Release internal_lock.
+void ConditionVariable::TimedWait(const base::TimeDelta& max_time) {
+  DWORD timeout = static_cast<DWORD>(max_time.InMilliseconds());
 
-  {
-    AutoUnlock unlock(user_lock_);  // Release caller's lock
-    WaitForSingleObject(handle, static_cast<DWORD>(max_time.InMilliseconds()));
-    // Minimize spurious signal creation window by recycling asap.
-    AutoLock auto_lock(internal_lock_);
-    RecycleEvent(waiting_event);
-    // Release internal_lock_
-  }  // Reacquire callers lock to depth at entry.
+  if (!SleepConditionVariableSRW(&cv_, srwlock_, timeout, 0)) {
+    // On failure, we only expect the CV to timeout. Any other error value means
+    // that we've unexpectedly woken up.
+    // Note that WAIT_TIMEOUT != ERROR_TIMEOUT. WAIT_TIMEOUT is used with the
+    // WaitFor* family of functions as a direct return value. ERROR_TIMEOUT is
+    // used with GetLastError().
+    DCHECK_EQ(static_cast<DWORD>(ERROR_TIMEOUT), GetLastError());
+  }
 }
 
-// Broadcast() is guaranteed to signal all threads that were waiting (i.e., had
-// a cv_event internally allocated for them) before Broadcast() was called.
 void ConditionVariable::Broadcast() {
-  std::stack<HANDLE> handles;  // See FAQ-question-10.
-  {
-    AutoLock auto_lock(internal_lock_);
-    if (waiting_list_.IsEmpty())
-      return;
-    while (!waiting_list_.IsEmpty())
-      // This is not a leak from waiting_list_.  See FAQ-question 12.
-      handles.push(waiting_list_.PopBack()->handle());
-  }  // Release internal_lock_.
-  while (!handles.empty()) {
-    SetEvent(handles.top());
-    handles.pop();
-  }
+  WakeAllConditionVariable(&cv_);
 }
 
-// Signal() will select one of the waiting threads, and signal it (signal its
-// cv_event).  For better performance we signal the thread that went to sleep
-// most recently (LIFO).  If we want fairness, then we wake the thread that has
-// been sleeping the longest (FIFO).
 void ConditionVariable::Signal() {
-  HANDLE handle;
-  {
-    AutoLock auto_lock(internal_lock_);
-    if (waiting_list_.IsEmpty())
-      return;  // No one to signal.
-    // Only performance option should be used.
-    // This is not a leak from waiting_list.  See FAQ-question 12.
-     handle = waiting_list_.PopBack()->handle();  // LIFO.
-  }  // Release internal_lock_.
-  SetEvent(handle);
-}
-
-// GetEventForWaiting() provides a unique cv_event for any caller that needs to
-// wait.  This means that (worst case) we may over time create as many cv_event
-// objects as there are threads simultaneously using this instance's Wait()
-// functionality.
-ConditionVariable::Event* ConditionVariable::GetEventForWaiting() {
-  // We hold internal_lock, courtesy of Wait().
-  Event* cv_event;
-  if (0 == recycling_list_size_) {
-    DCHECK(recycling_list_.IsEmpty());
-    cv_event = new Event();
-    cv_event->InitListElement();
-    allocation_counter_++;
-    // CHECK_NE is not defined in our codebase, so we have to use CHECK
-    CHECK(cv_event->handle());
-  } else {
-    cv_event = recycling_list_.PopFront();
-    recycling_list_size_--;
-  }
-  waiting_list_.PushBack(cv_event);
-  return cv_event;
-}
-
-// RecycleEvent() takes a cv_event that was previously used for Wait()ing, and
-// recycles it for use in future Wait() calls for this or other threads.
-// Note that there is a tiny chance that the cv_event is still signaled when we
-// obtain it, and that can cause spurious signals (if/when we re-use the
-// cv_event), but such is quite rare (see FAQ-question-5).
-void ConditionVariable::RecycleEvent(Event* used_event) {
-  // We hold internal_lock, courtesy of Wait().
-  // If the cv_event timed out, then it is necessary to remove it from
-  // waiting_list_.  If it was selected by Broadcast() or Signal(), then it is
-  // already gone.
-  used_event->Extract();  // Possibly redundant
-  recycling_list_.PushBack(used_event);
-  recycling_list_size_++;
-}
-//------------------------------------------------------------------------------
-// The next section provides the implementation for the private Event class.
-//------------------------------------------------------------------------------
-
-// Event provides a doubly-linked-list of events for use exclusively by the
-// ConditionVariable class.
-
-// This custom container was crafted because no simple combination of STL
-// classes appeared to support the functionality required.  The specific
-// unusual requirement for a linked-list-class is support for the Extract()
-// method, which can remove an element from a list, potentially for insertion
-// into a second list.  Most critically, the Extract() method is idempotent,
-// turning the indicated element into an extracted singleton whether it was
-// contained in a list or not.  This functionality allows one (or more) of
-// threads to do the extraction.  The iterator that identifies this extractable
-// element (in this case, a pointer to the list element) can be used after
-// arbitrary manipulation of the (possibly) enclosing list container.  In
-// general, STL containers do not provide iterators that can be used across
-// modifications (insertions/extractions) of the enclosing containers, and
-// certainly don't provide iterators that can be used if the identified
-// element is *deleted* (removed) from the container.
-
-// It is possible to use multiple redundant containers, such as an STL list,
-// and an STL map, to achieve similar container semantics.  This container has
-// only O(1) methods, while the corresponding (multiple) STL container approach
-// would have more complex O(log(N)) methods (yeah... N isn't that large).
-// Multiple containers also makes correctness more difficult to assert, as
-// data is redundantly stored and maintained, which is generally evil.
-
-ConditionVariable::Event::Event() : handle_(0) {
-  next_ = prev_ = this;  // Self referencing circular.
-}
-
-ConditionVariable::Event::~Event() {
-  if (0 == handle_) {
-    // This is the list holder
-    while (!IsEmpty()) {
-      Event* cv_event = PopFront();
-      DCHECK(cv_event->ValidateAsItem());
-      delete cv_event;
-    }
-  }
-  DCHECK(IsSingleton());
-  if (0 != handle_) {
-    int ret_val = CloseHandle(handle_);
-    DCHECK(ret_val);
-  }
-}
-
-// Change a container instance permanently into an element of a list.
-void ConditionVariable::Event::InitListElement() {
-  DCHECK(!handle_);
-  handle_ = CreateEvent(NULL, false, false, NULL);
-  CHECK(handle_);
-}
-
-// Methods for use on lists.
-bool ConditionVariable::Event::IsEmpty() const {
-  DCHECK(ValidateAsList());
-  return IsSingleton();
-}
-
-void ConditionVariable::Event::PushBack(Event* other) {
-  DCHECK(ValidateAsList());
-  DCHECK(other->ValidateAsItem());
-  DCHECK(other->IsSingleton());
-  // Prepare other for insertion.
-  other->prev_ = prev_;
-  other->next_ = this;
-  // Cut into list.
-  prev_->next_ = other;
-  prev_ = other;
-  DCHECK(ValidateAsDistinct(other));
-}
-
-ConditionVariable::Event* ConditionVariable::Event::PopFront() {
-  DCHECK(ValidateAsList());
-  DCHECK(!IsSingleton());
-  return next_->Extract();
-}
-
-ConditionVariable::Event* ConditionVariable::Event::PopBack() {
-  DCHECK(ValidateAsList());
-  DCHECK(!IsSingleton());
-  return prev_->Extract();
-}
-
-// Methods for use on list elements.
-// Accessor method.
-HANDLE ConditionVariable::Event::handle() const {
-  DCHECK(ValidateAsItem());
-  return handle_;
-}
-
-// Pull an element from a list (if it's in one).
-ConditionVariable::Event* ConditionVariable::Event::Extract() {
-  DCHECK(ValidateAsItem());
-  if (!IsSingleton()) {
-    // Stitch neighbors together.
-    next_->prev_ = prev_;
-    prev_->next_ = next_;
-    // Make extractee into a singleton.
-    prev_ = next_ = this;
-  }
-  DCHECK(IsSingleton());
-  return this;
-}
-
-// Method for use on a list element or on a list.
-bool ConditionVariable::Event::IsSingleton() const {
-  DCHECK(ValidateLinks());
-  return next_ == this;
-}
-
-// Provide pre/post conditions to validate correct manipulations.
-bool ConditionVariable::Event::ValidateAsDistinct(Event* other) const {
-  return ValidateLinks() && other->ValidateLinks() && (this != other);
-}
-
-bool ConditionVariable::Event::ValidateAsItem() const {
-  return (0 != handle_) && ValidateLinks();
-}
-
-bool ConditionVariable::Event::ValidateAsList() const {
-  return (0 == handle_) && ValidateLinks();
+  WakeConditionVariable(&cv_);
 }
 
-bool ConditionVariable::Event::ValidateLinks() const {
-  // Make sure both of our neighbors have links that point back to us.
-  // We don't do the O(n) check and traverse the whole loop, and instead only
-  // do a local check to (and returning from) our immediate neighbors.
-  return (next_->prev_ == this) && (prev_->next_ == this);
-}
-
-
-/*
-FAQ On subtle implementation details:
-
-1) What makes this problem subtle?  Please take a look at "Strategies
-for Implementing POSIX Condition Variables on Win32" by Douglas
-C. Schmidt and Irfan Pyarali.
-http://www.cs.wustl.edu/~schmidt/win32-cv-1.html It includes
-discussions of numerous flawed strategies for implementing this
-functionality.  I'm not convinced that even the final proposed
-implementation has semantics that are as nice as this implementation
-(especially with regard to Broadcast() and the impact on threads that
-try to Wait() after a Broadcast() has been called, but before all the
-original waiting threads have been signaled).
-
-2) Why can't you use a single wait_event for all threads that call
-Wait()?  See FAQ-question-1, or consider the following: If a single
-event were used, then numerous threads calling Wait() could release
-their cs locks, and be preempted just before calling
-WaitForSingleObject().  If a call to Broadcast() was then presented on
-a second thread, it would be impossible to actually signal all
-waiting(?) threads.  Some number of SetEvent() calls *could* be made,
-but there could be no guarantee that those led to to more than one
-signaled thread (SetEvent()'s may be discarded after the first!), and
-there could be no guarantee that the SetEvent() calls didn't just
-awaken "other" threads that hadn't even started waiting yet (oops).
-Without any limit on the number of requisite SetEvent() calls, the
-system would be forced to do many such calls, allowing many new waits
-to receive spurious signals.
-
-3) How does this implementation cause spurious signal events?  The
-cause in this implementation involves a race between a signal via
-time-out and a signal via Signal() or Broadcast().  The series of
-actions leading to this are:
-
-a) Timer fires, and a waiting thread exits the line of code:
-
-    WaitForSingleObject(waiting_event, max_time.InMilliseconds());
-
-b) That thread (in (a)) is randomly pre-empted after the above line,
-leaving the waiting_event reset (unsignaled) and still in the
-waiting_list_.
-
-c) A call to Signal() (or Broadcast()) on a second thread proceeds, and
-selects the waiting cv_event (identified in step (b)) as the event to revive
-via a call to SetEvent().
-
-d) The Signal() method (step c) calls SetEvent() on waiting_event (step b).
-
-e) The waiting cv_event (step b) is now signaled, but no thread is
-waiting on it.
-
-f) When that waiting_event (step b) is reused, it will immediately
-be signaled (spuriously).
-
-
-4) Why do you recycle events, and cause spurious signals?  First off,
-the spurious events are very rare.  They can only (I think) appear
-when the race described in FAQ-question-3 takes place.  This should be
-very rare.  Most(?)  uses will involve only timer expiration, or only
-Signal/Broadcast() actions.  When both are used, it will be rare that
-the race will appear, and it would require MANY Wait() and signaling
-activities.  If this implementation did not recycle events, then it
-would have to create and destroy events for every call to Wait().
-That allocation/deallocation and associated construction/destruction
-would be costly (per wait), and would only be a rare benefit (when the
-race was "lost" and a spurious signal took place). That would be bad
-(IMO) optimization trade-off.  Finally, such spurious events are
-allowed by the specification of condition variables (such as
-implemented in Vista), and hence it is better if any user accommodates
-such spurious events (see usage note in condition_variable.h).
-
-5) Why don't you reset events when you are about to recycle them, or
-about to reuse them, so that the spurious signals don't take place?
-The thread described in FAQ-question-3 step c may be pre-empted for an
-arbitrary length of time before proceeding to step d.  As a result,
-the wait_event may actually be re-used *before* step (e) is reached.
-As a result, calling reset would not help significantly.
-
-6) How is it that the callers lock is released atomically with the
-entry into a wait state?  We commit to the wait activity when we
-allocate the wait_event for use in a given call to Wait().  This
-allocation takes place before the caller's lock is released (and
-actually before our internal_lock_ is released).  That allocation is
-the defining moment when "the wait state has been entered," as that
-thread *can* now be signaled by a call to Broadcast() or Signal().
-Hence we actually "commit to wait" before releasing the lock, making
-the pair effectively atomic.
-
-8) Why do you need to lock your data structures during waiting, as the
-caller is already in possession of a lock?  We need to Acquire() and
-Release() our internal lock during Signal() and Broadcast().  If we tried
-to use a callers lock for this purpose, we might conflict with their
-external use of the lock.  For example, the caller may use to consistently
-hold a lock on one thread while calling Signal() on another, and that would
-block Signal().
-
-9) Couldn't a more efficient implementation be provided if you
-preclude using more than one external lock in conjunction with a
-single ConditionVariable instance?  Yes, at least it could be viewed
-as a simpler API (since you don't have to reiterate the lock argument
-in each Wait() call).  One of the constructors now takes a specific
-lock as an argument, and a there are corresponding Wait() calls that
-don't specify a lock now.  It turns that the resulting implmentation
-can't be made more efficient, as the internal lock needs to be used by
-Signal() and Broadcast(), to access internal data structures.  As a
-result, I was not able to utilize the user supplied lock (which is
-being used by the user elsewhere presumably) to protect the private
-member access.
-
-9) Since you have a second lock, how can be be sure that there is no
-possible deadlock scenario?  Our internal_lock_ is always the last
-lock acquired, and the first one released, and hence a deadlock (due
-to critical section problems) is impossible as a consequence of our
-lock.
-
-10) When doing a Broadcast(), why did you copy all the events into
-an STL queue, rather than making a linked-loop, and iterating over it?
-The iterating during Broadcast() is done so outside the protection
-of the internal lock. As a result, other threads, such as the thread
-wherein a related event is waiting, could asynchronously manipulate
-the links around a cv_event.  As a result, the link structure cannot
-be used outside a lock.  Broadcast() could iterate over waiting
-events by cycling in-and-out of the protection of the internal_lock,
-but that appears more expensive than copying the list into an STL
-stack.
-
-11) Why did the lock.h file need to be modified so much for this
-change?  Central to a Condition Variable is the atomic release of a
-lock during a Wait().  This places Wait() functionality exactly
-mid-way between the two classes, Lock and Condition Variable.  Given
-that there can be nested Acquire()'s of locks, and Wait() had to
-Release() completely a held lock, it was necessary to augment the Lock
-class with a recursion counter. Even more subtle is the fact that the
-recursion counter (in a Lock) must be protected, as many threads can
-access it asynchronously.  As a positive fallout of this, there are
-now some DCHECKS to be sure no one Release()s a Lock more than they
-Acquire()ed it, and there is ifdef'ed functionality that can detect
-nested locks (legal under windows, but not under Posix).
-
-12) Why is it that the cv_events removed from list in Broadcast() and Signal()
-are not leaked?  How are they recovered??  The cv_events that appear to leak are
-taken from the waiting_list_.  For each element in that list, there is currently
-a thread in or around the WaitForSingleObject() call of Wait(), and those
-threads have references to these otherwise leaked events. They are passed as
-arguments to be recycled just aftre returning from WaitForSingleObject().
-
-13) Why did you use a custom container class (the linked list), when STL has
-perfectly good containers, such as an STL list?  The STL list, as with any
-container, does not guarantee the utility of an iterator across manipulation
-(such as insertions and deletions) of the underlying container.  The custom
-double-linked-list container provided that assurance.  I don't believe any
-combination of STL containers provided the services that were needed at the same
-O(1) efficiency as the custom linked list.  The unusual requirement
-for the container class is that a reference to an item within a container (an
-iterator) needed to be maintained across an arbitrary manipulation of the
-container.  This requirement exposes itself in the Wait() method, where a
-waiting_event must be selected prior to the WaitForSingleObject(), and then it
-must be used as part of recycling to remove the related instance from the
-waiting_list.  A hash table (STL map) could be used, but I was embarrased to
-use a complex and relatively low efficiency container when a doubly linked list
-provided O(1) performance in all required operations.  Since other operations
-to provide performance-and/or-fairness required queue (FIFO) and list (LIFO)
-containers, I would also have needed to use an STL list/queue as well as an STL
-map.  In the end I decided it would be "fun" to just do it right, and I
-put so many assertions (DCHECKs) into the container class that it is trivial to
-code review and validate its correctness.
-
-*/
diff --git a/ipc/chromium/src/base/lock.cc b/ipc/chromium/src/base/lock.cc
deleted file mode 100644
index a34d3726e0..0000000000
--- a/ipc/chromium/src/base/lock.cc
+++ /dev/null
@@ -1,8 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Lock class.
-
-// Depricated file.  See lock_impl_*.cc for platform specific versions.
diff --git a/ipc/chromium/src/base/lock.h b/ipc/chromium/src/base/lock.h
index 66fb110002..236c2a1925 100644
--- a/ipc/chromium/src/base/lock.h
+++ b/ipc/chromium/src/base/lock.h
@@ -1,38 +1,60 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_LOCK_H_
 #define BASE_LOCK_H_
 
+#include "base/basictypes.h"
 #include "base/lock_impl.h"
+#include "base/platform_thread.h"
+#include "build/build_config.h"
 
 // A convenient wrapper for an OS specific critical section.
-
 class Lock {
  public:
+   // Optimized wrapper implementation
   Lock() : lock_() {}
   ~Lock() {}
   void Acquire() { lock_.Lock(); }
   void Release() { lock_.Unlock(); }
+
   // If the lock is not held, take it and return true. If the lock is already
-  // held by another thread, immediately return false.
+  // held by another thread, immediately return false. This must not be called
+  // by a thread already holding the lock (what happens is undefined and an
+  // assertion may fail).
   bool Try() { return lock_.Try(); }
 
-  // In debug builds this method checks that the lock has been acquired by the
-  // calling thread.  If the lock has not been acquired, then the method
-  // will DCHECK().  In non-debug builds, the LockImpl's implementation of
-  // AssertAcquired() is an empty inline method.
-  void AssertAcquired() const { return lock_.AssertAcquired(); }
+  // Null implementation if not debug.
+  void AssertAcquired() const {}
+
+  // Whether Lock mitigates priority inversion when used from different thread
+  // priorities.
+  static bool HandlesMultipleThreadPriorities() {
+#if defined(OS_POSIX)
+    // POSIX mitigates priority inversion by setting the priority of a thread
+    // holding a Lock to the maximum priority of any other thread waiting on it.
+    return base::internal::LockImpl::PriorityInheritanceAvailable();
+#elif defined(OS_WIN)
+    // Windows mitigates priority inversion by randomly boosting the priority of
+    // ready threads.
+    // https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx
+    return true;
+#else
+#error Unsupported platform
+#endif
+  }
 
-  // Return the underlying lock implementation.
-  // TODO(awalker): refactor lock and condition variables so that this is
-  // unnecessary.
-  LockImpl* lock_impl() { return &lock_; }
+#if defined(OS_POSIX) || defined(OS_WIN)
+  // Both Windows and POSIX implementations of ConditionVariable need to be
+  // able to see our lock and tweak our debugging counters, as they release and
+  // acquire locks inside of their condition variable APIs.
+  friend class ConditionVariable;
+#endif
 
  private:
-  LockImpl lock_;  // Platform specific underlying lock implementation.
+  // Platform specific underlying lock implementation.
+  ::base::internal::LockImpl lock_;
 
   DISALLOW_COPY_AND_ASSIGN(Lock);
 };
@@ -40,10 +62,16 @@ class Lock {
 // A helper class that acquires the given Lock while the AutoLock is in scope.
 class AutoLock {
  public:
+  struct AlreadyAcquired {};
+
   explicit AutoLock(Lock& lock) : lock_(lock) {
     lock_.Acquire();
   }
 
+  AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
+    lock_.AssertAcquired();
+  }
+
   ~AutoLock() {
     lock_.AssertAcquired();
     lock_.Release();
diff --git a/ipc/chromium/src/base/lock_impl.h b/ipc/chromium/src/base/lock_impl.h
index 67105bd57c..a9a52d4b79 100644
--- a/ipc/chromium/src/base/lock_impl.h
+++ b/ipc/chromium/src/base/lock_impl.h
@@ -1,11 +1,11 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_LOCK_IMPL_H_
 #define BASE_LOCK_IMPL_H_
 
+#include "base/basictypes.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
@@ -14,8 +14,8 @@
 #include <pthread.h>
 #endif
 
-#include "base/basictypes.h"
-#include "base/platform_thread.h"
+namespace base {
+namespace internal {
 
 // This class implements the underlying platform-specific spin-lock mechanism
 // used for the Lock class.  Most users should not use LockImpl directly, but
@@ -23,9 +23,9 @@
 class LockImpl {
  public:
 #if defined(OS_WIN)
-  typedef CRITICAL_SECTION OSLockType;
+  using NativeHandle = SRWLOCK;
 #elif defined(OS_POSIX)
-  typedef pthread_mutex_t OSLockType;
+  using NativeHandle =  pthread_mutex_t;
 #endif
 
   LockImpl();
@@ -42,37 +42,23 @@ class LockImpl {
   // a successful call to Try, or a call to Lock.
   void Unlock();
 
-  // Debug-only method that will DCHECK() if the lock is not acquired by the
-  // current thread.  In non-debug builds, no check is performed.
-  // Because linux and mac condition variables modify the underlyning lock
-  // through the os_lock() method, runtime assertions can not be done on those
-  // builds.
-#if defined(NDEBUG) || !defined(OS_WIN)
-  void AssertAcquired() const {}
-#else
-  void AssertAcquired() const;
-#endif
-
-  // Return the native underlying lock.  Not supported for Windows builds.
+  // Return the native underlying lock.  
   // TODO(awalker): refactor lock and condition variables so that this is
   // unnecessary.
-#if !defined(OS_WIN)
-  OSLockType* os_lock() { return &os_lock_; }
+  NativeHandle* native_handle() { return &native_handle_; }
+
+#if defined(OS_POSIX)
+  // Whether this lock will attempt to use priority inheritance.
+  static bool PriorityInheritanceAvailable();
 #endif
 
  private:
-  OSLockType os_lock_;
-
-#if !defined(NDEBUG) && defined(OS_WIN)
-  // All private data is implicitly protected by lock_.
-  // Be VERY careful to only access members under that lock.
-  PlatformThreadId owning_thread_id_;
-  int32_t recursion_count_shadow_;
-  bool recursion_used_;      // Allow debugging to continued after a DCHECK().
-#endif  // NDEBUG
+  NativeHandle native_handle_;
 
   DISALLOW_COPY_AND_ASSIGN(LockImpl);
 };
 
+}  // namespace internal
+}  // namespace base
 
 #endif  // BASE_LOCK_IMPL_H_
diff --git a/ipc/chromium/src/base/lock_impl_posix.cc b/ipc/chromium/src/base/lock_impl_posix.cc
index 0513cf0e65..b0fbfe5f04 100644
--- a/ipc/chromium/src/base/lock_impl_posix.cc
+++ b/ipc/chromium/src/base/lock_impl_posix.cc
@@ -1,49 +1,85 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/lock_impl.h"
 
 #include <errno.h>
+#include <string.h>
 
 #include "base/logging.h"
+#include "base/lock.h"
+
+namespace base {
+namespace internal {
+
+#define PRIORITY_INHERITANCE_LOCKS_POSSIBLE() 1
 
 LockImpl::LockImpl() {
-#ifndef NDEBUG
-  // In debug, setup attributes for lock error checking.
   pthread_mutexattr_t mta;
   int rv = pthread_mutexattr_init(&mta);
-  DCHECK_EQ(rv, 0);
+
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
+#if PRIORITY_INHERITANCE_LOCKS_POSSIBLE()
+  if (PriorityInheritanceAvailable()) {
+    rv = pthread_mutexattr_setprotocol(&mta, PTHREAD_PRIO_INHERIT);
+    DCHECK_EQ(rv, 0) << ". " << strerror(rv);
+  }
+#endif
+#ifndef NDEBUG
+  // In debug, setup attributes for lock error checking.
   rv = pthread_mutexattr_settype(&mta, PTHREAD_MUTEX_ERRORCHECK);
-  DCHECK_EQ(rv, 0);
-  rv = pthread_mutex_init(&os_lock_, &mta);
-  DCHECK_EQ(rv, 0);
-  rv = pthread_mutexattr_destroy(&mta);
-  DCHECK_EQ(rv, 0);
-#else
-  // In release, go with the default lock attributes.
-  pthread_mutex_init(&os_lock_, NULL);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
 #endif
+  rv = pthread_mutex_init(&native_handle_, &mta);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
+  rv = pthread_mutexattr_destroy(&mta);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
 }
 
 LockImpl::~LockImpl() {
-  int rv = pthread_mutex_destroy(&os_lock_);
-  DCHECK_EQ(rv, 0);
+  int rv = pthread_mutex_destroy(&native_handle_);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
 }
 
 bool LockImpl::Try() {
-  int rv = pthread_mutex_trylock(&os_lock_);
-  DCHECK(rv == 0 || rv == EBUSY);
-  return rv == 0;
+  int rv = pthread_mutex_trylock(&native_handle_);
+  DCHECK(rv == 0 || rv == EBUSY) << ". " << strerror(rv);
 }
 
 void LockImpl::Lock() {
-  int rv = pthread_mutex_lock(&os_lock_);
-  DCHECK_EQ(rv, 0);
+  int rv = pthread_mutex_lock(&native_handle_);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
 }
 
 void LockImpl::Unlock() {
-  int rv = pthread_mutex_unlock(&os_lock_);
-  DCHECK_EQ(rv, 0);
+  int rv = pthread_mutex_unlock(&native_handle_);
+  DCHECK_EQ(rv, 0) << ". " << strerror(rv);
+}
+
+// static
+bool LockImpl::PriorityInheritanceAvailable() {
+#if PRIORITY_INHERITANCE_LOCKS_POSSIBLE() && defined(OS_MACOSX)
+  return true;
+#else
+  // Security concerns prevent the use of priority inheritance mutexes on Linux.
+  //   * CVE-2010-0622 - wake_futex_pi unlocks incorrect, possible DoS.
+  //     https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-0622
+  //   * CVE-2012-6647 - Linux < 3.5.1, futex_wait_requeue_pi possible DoS.
+  //     https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-6647
+  //   * CVE-2014-3153 - Linux <= 3.14.5, futex_requeue, privilege escalation.
+  //     https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-3153
+  //
+  // If the above were all addressed, we still need a runtime check to deal with
+  // the bug below.
+  //   * glibc Bug 14652: https://sourceware.org/bugzilla/show_bug.cgi?id=14652
+  //     Fixed in glibc 2.17.
+  //     Priority inheritance mutexes may deadlock with condition variables
+  //     during recacquisition of the mutex after the condition variable is
+  //     signalled.
+  return false;
+#endif
 }
+
+}  // namespace internal
+}  // namespace base
diff --git a/ipc/chromium/src/base/lock_impl_win.cc b/ipc/chromium/src/base/lock_impl_win.cc
index 17d72ea962..c8f2191441 100644
--- a/ipc/chromium/src/base/lock_impl_win.cc
+++ b/ipc/chromium/src/base/lock_impl_win.cc
@@ -1,74 +1,27 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/lock_impl.h"
-#include "base/logging.h"
 
-// NOTE: Although windows critical sections support recursive locks, we do not
-// allow this, and we will commonly fire a DCHECK() if a thread attempts to
-// acquire the lock a second time (while already holding it).
+namespace base {
+namespace internal {
 
-LockImpl::LockImpl() {
-#ifndef NDEBUG
-  recursion_count_shadow_ = 0;
-  recursion_used_ = false;
-  owning_thread_id_ = 0;
-#endif  // NDEBUG
-  // The second parameter is the spin count, for short-held locks it avoid the
-  // contending thread from going to sleep which helps performance greatly.
-  ::InitializeCriticalSectionAndSpinCount(&os_lock_, 2000);
-}
+LockImpl::LockImpl() : native_handle_(SRWLOCK_INIT) {}
 
-LockImpl::~LockImpl() {
-  ::DeleteCriticalSection(&os_lock_);
-}
+LockImpl::~LockImpl() = default;
 
 bool LockImpl::Try() {
-  if (::TryEnterCriticalSection(&os_lock_) != FALSE) {
-#ifndef NDEBUG
-    // ONLY access data after locking.
-    owning_thread_id_ = PlatformThread::CurrentId();
-    DCHECK_NE(owning_thread_id_, 0);
-    recursion_count_shadow_++;
-    if (2 == recursion_count_shadow_ && !recursion_used_) {
-      recursion_used_ = true;
-      DCHECK(false);  // Catch accidental redundant lock acquisition.
-    }
-#endif
-    return true;
-  }
-  return false;
+  return !!::TryAcquireSRWLockExclusive(&native_handle_);
 }
 
 void LockImpl::Lock() {
-  ::EnterCriticalSection(&os_lock_);
-#ifndef NDEBUG
-  // ONLY access data after locking.
-  owning_thread_id_ = PlatformThread::CurrentId();
-  DCHECK_NE(owning_thread_id_, 0);
-  recursion_count_shadow_++;
-  if (2 == recursion_count_shadow_ && !recursion_used_) {
-    recursion_used_ = true;
-    DCHECK(false);  // Catch accidental redundant lock acquisition.
-  }
-#endif  // NDEBUG
+  ::AcquireSRWLockExclusive(&native_handle_);
 }
 
 void LockImpl::Unlock() {
-#ifndef NDEBUG
-  --recursion_count_shadow_;  // ONLY access while lock is still held.
-  DCHECK(0 <= recursion_count_shadow_);
-  owning_thread_id_ = 0;
-#endif  // NDEBUG
-  ::LeaveCriticalSection(&os_lock_);
+  ::ReleaseSRWLockExclusive(&native_handle_);
 }
 
-// In non-debug builds, this method is declared as an empty inline method.
-#ifndef NDEBUG
-void LockImpl::AssertAcquired() const {
-  DCHECK(recursion_count_shadow_ > 0);
-  DCHECK_EQ(owning_thread_id_, PlatformThread::CurrentId());
-}
-#endif
+}  // namespace internal
+}  // namespace base