ipc/glue/CrossProcessMutex_posix.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "CrossProcessMutex.h"
   8 #include "mozilla/Unused.h"
   9 #include "nsDebug.h"
  10 #include "nsISupportsImpl.h"
  11
  12 namespace {
  13
  14 struct MutexData {
  15   pthread_mutex_t mMutex;
  16   mozilla::Atomic<int32_t> mCount;
  17 };
  18
  19 }  // namespace
  20
  21 namespace mozilla {
  22
  23 static void InitMutex(pthread_mutex_t* mMutex) {
  24   pthread_mutexattr_t mutexAttributes;
  25   pthread_mutexattr_init(&mutexAttributes);
  26   // Make the mutex reentrant so it behaves the same as a win32 mutex
  27   if (pthread_mutexattr_settype(&mutexAttributes, PTHREAD_MUTEX_RECURSIVE)) {
  28     MOZ_CRASH();
  29   }
  30   if (pthread_mutexattr_setpshared(&mutexAttributes, PTHREAD_PROCESS_SHARED)) {
  31     MOZ_CRASH();
  32   }
  33
  34   if (pthread_mutex_init(mMutex, &mutexAttributes)) {
  35     MOZ_CRASH();
  36   }
  37 }
  38
  39 CrossProcessMutex::CrossProcessMutex(const char*)
  40     : mMutex(nullptr), mCount(nullptr) {
  41 #if defined(MOZ_SANDBOX)
  42   // POSIX mutexes in shared memory aren't guaranteed to be safe - and
  43   // they specifically are not on Linux.
  44   MOZ_RELEASE_ASSERT(false);
  45 #endif
  46   mSharedBuffer = new ipc::SharedMemoryBasic;
  47   if (!mSharedBuffer->Create(sizeof(MutexData))) {
  48     MOZ_CRASH();
  49   }
  50
  51   if (!mSharedBuffer->Map(sizeof(MutexData))) {
  52     MOZ_CRASH();
  53   }
  54
  55   MutexData* data = static_cast<MutexData*>(mSharedBuffer->memory());
  56
  57   if (!data) {
  58     MOZ_CRASH();
  59   }
  60
  61   mMutex = &(data->mMutex);
  62   mCount = &(data->mCount);
  63
  64   *mCount = 1;
  65   InitMutex(mMutex);
  66
  67   MOZ_COUNT_CTOR(CrossProcessMutex);
  68 }
  69
  70 CrossProcessMutex::CrossProcessMutex(CrossProcessMutexHandle aHandle)
  71     : mMutex(nullptr), mCount(nullptr) {
  72   mSharedBuffer = new ipc::SharedMemoryBasic;
  73
  74   if (!mSharedBuffer->IsHandleValid(aHandle)) {
  75     MOZ_CRASH();
  76   }
  77
  78   if (!mSharedBuffer->SetHandle(std::move(aHandle),
  79                                 ipc::SharedMemory::RightsReadWrite)) {
  80     MOZ_CRASH();
  81   }
  82
  83   if (!mSharedBuffer->Map(sizeof(MutexData))) {
  84     MOZ_CRASH();
  85   }
  86
  87   MutexData* data = static_cast<MutexData*>(mSharedBuffer->memory());
  88
  89   if (!data) {
  90     MOZ_CRASH();
  91   }
  92
  93   mMutex = &(data->mMutex);
  94   mCount = &(data->mCount);
  95   int32_t count = (*mCount)++;
  96
  97   if (count == 0) {
  98     // The other side has already let go of their CrossProcessMutex, so now
  99     // mMutex is garbage. We need to re-initialize it.
 100     InitMutex(mMutex);
 101   }
 102
 103   MOZ_COUNT_CTOR(CrossProcessMutex);
 104 }
 105
 106 CrossProcessMutex::~CrossProcessMutex() {
 107   int32_t count = --(*mCount);
 108
 109   if (count == 0) {
 110     // Nothing can be done if the destroy fails so ignore return code.
 111     Unused << pthread_mutex_destroy(mMutex);
 112   }
 113
 114   MOZ_COUNT_DTOR(CrossProcessMutex);
 115 }
 116
 117 void CrossProcessMutex::Lock() {
 118   MOZ_ASSERT(*mCount > 0, "Attempting to lock mutex with zero ref count");
 119   pthread_mutex_lock(mMutex);
 120 }
 121
 122 void CrossProcessMutex::Unlock() {
 123   MOZ_ASSERT(*mCount > 0, "Attempting to unlock mutex with zero ref count");
 124   pthread_mutex_unlock(mMutex);
 125 }
 126
 127 CrossProcessMutexHandle CrossProcessMutex::CloneHandle() {
 128   CrossProcessMutexHandle result = ipc::SharedMemoryBasic::NULLHandle();
 129
 130   if (mSharedBuffer) {
 131     result = mSharedBuffer->CloneHandle();
 132     if (!result) {
 133       MOZ_CRASH();
 134     }
 135   }
 136
 137   return result;
 138 }
 139
 140 }  // namespace mozilla