ipc/glue/CrossProcessMutex_posix.cpp
author Kartikaya Gupta <kgupta@mozilla.com>
Fri, 20 Jun 2014 17:06:36 -0400
changeset 195554 04303003b89691a86dee436cc152340ba2bf1d14
parent 176239 cfaa46b8361246d7defd3f8b5d4dc482f844aeb2
child 203402 74034d6b6ae6d550c6b482bd79a595f8c527d87d
permissions -rw-r--r--
Bug 1024728 - Gracefully handle a CrossProcessMutex being initialized with a stale handle. r=khuey, a=lmandel

/* -*- 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 {

static void
InitMutex(pthread_mutex_t* mMutex)
{
  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();
  }
}

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;
  InitMutex(mMutex);

  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);
  int32_t count = (*mCount)++;

  if (count == 0) {
    // The other side has already let go of their CrossProcessMutex, so now
    // mMutex is garbage. We need to re-initialize it.
    InitMutex(mMutex);
  }

  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;
}

}