diff -r 000000000000 -r 6474c204b198 ipc/glue/CrossProcessMutex_posix.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/glue/CrossProcessMutex_posix.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,131 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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 "CrossProcessMutex.h"
+#include "mozilla/unused.h"
+#include "nsDebug.h"
+#include "nsISupportsImpl.h"
+
+namespace {
+
+struct MutexData {
+  pthread_mutex_t mMutex;
+  mozilla::Atomic<int32_t> mCount;
+};
+
+}
+
+namespace mozilla {
+
+CrossProcessMutex::CrossProcessMutex(const char*)
+    : mSharedBuffer(nullptr)
+    , mMutex(nullptr)
+    , mCount(nullptr)
+{
+  mSharedBuffer = new ipc::SharedMemoryBasic;
+  if (!mSharedBuffer->Create(sizeof(MutexData))) {
+    MOZ_CRASH();
+  }
+
+  if (!mSharedBuffer->Map(sizeof(MutexData))) {
+    MOZ_CRASH();
+  }
+
+  MutexData* data = static_cast<MutexData*>(mSharedBuffer->memory());
+
+  if (!data) {
+    MOZ_CRASH();
+  }
+
+  mMutex = &(data->mMutex);
+  mCount = &(data->mCount);
+
+  *mCount = 1;
+
+  pthread_mutexattr_t mutexAttributes;
+  pthread_mutexattr_init(&mutexAttributes);
+  // Make the mutex reentrant so it behaves the same as a win32 mutex
+  if (pthread_mutexattr_settype(&mutexAttributes, PTHREAD_MUTEX_RECURSIVE)) {
+    MOZ_CRASH();
+  }
+  if (pthread_mutexattr_setpshared(&mutexAttributes, PTHREAD_PROCESS_SHARED)) {
+    MOZ_CRASH();
+  }
+
+  if (pthread_mutex_init(mMutex, &mutexAttributes)) {
+    MOZ_CRASH();
+  }
+
+  MOZ_COUNT_CTOR(CrossProcessMutex);
+}
+
+CrossProcessMutex::CrossProcessMutex(CrossProcessMutexHandle aHandle)
+    : mSharedBuffer(nullptr)
+    , mMutex(nullptr)
+    , mCount(nullptr)
+{
+  if (!ipc::SharedMemoryBasic::IsHandleValid(aHandle)) {
+    MOZ_CRASH();
+  }
+
+  mSharedBuffer = new ipc::SharedMemoryBasic(aHandle);
+
+  if (!mSharedBuffer->Map(sizeof(MutexData))) {
+    MOZ_CRASH();
+  }
+
+  MutexData* data = static_cast<MutexData*>(mSharedBuffer->memory());
+
+  if (!data) {
+    MOZ_CRASH();
+  }
+
+  mMutex = &(data->mMutex);
+  mCount = &(data->mCount);
+  (*mCount)++;
+
+  MOZ_COUNT_CTOR(CrossProcessMutex);
+}
+
+CrossProcessMutex::~CrossProcessMutex()
+{
+  int32_t count = --(*mCount);
+
+  if (count == 0) {
+    // Nothing can be done if the destroy fails so ignore return code.
+    unused << pthread_mutex_destroy(mMutex);
+  }
+
+  delete mSharedBuffer;
+  MOZ_COUNT_DTOR(CrossProcessMutex);
+}
+
+void
+CrossProcessMutex::Lock()
+{
+  MOZ_ASSERT(*mCount > 0, "Attempting to lock mutex with zero ref count");
+  pthread_mutex_lock(mMutex);
+}
+
+void
+CrossProcessMutex::Unlock()
+{
+  MOZ_ASSERT(*mCount > 0, "Attempting to unlock mutex with zero ref count");
+  pthread_mutex_unlock(mMutex);
+}
+
+CrossProcessMutexHandle
+CrossProcessMutex::ShareToProcess(base::ProcessHandle aHandle)
+{
+  CrossProcessMutexHandle result = ipc::SharedMemoryBasic::NULLHandle();
+
+  if (mSharedBuffer && !mSharedBuffer->ShareToProcess(aHandle, &result)) {
+    MOZ_CRASH();
+  }
+
+  return result;
+}
+
+}