Bug 1121297 (Part 2) - Make VolatileBuffer threadsafe. r=glandium

memory/volatile/VolatileBuffer.h

@@ -6,6 +6,7 @@
 #define mozalloc_VolatileBuffer_h
 
 #include "mozilla/mozalloc.h"
+#include "mozilla/Mutex.h"
 #include "mozilla/RefPtr.h"
 #include "mozilla/MemoryReporting.h"
 
@@ -36,19 +37,19 @@
  * When a buffer is purged, some or all of the buffer is zeroed out. This
  * API cannot tell which parts of the buffer were lost.
  *
- * VolatileBuffer is not thread safe. Do not use VolatileBufferPtrs on
+ * VolatileBuffer and VolatileBufferPtr are threadsafe.
- * different threads.
  */
 
 namespace mozilla {
 
-class VolatileBuffer : public RefCounted<VolatileBuffer>
+class VolatileBuffer
 {
   friend class VolatileBufferPtr_base;
 public:
   MOZ_DECLARE_REFCOUNTED_TYPENAME(VolatileBuffer)
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(VolatileBuffer)
+
   VolatileBuffer();
-  ~VolatileBuffer();
 
   /* aAlignment must be a multiple of the pointer size */
   bool Init(size_t aSize, size_t aAlignment = sizeof(void*));
@@ -62,6 +63,15 @@ protected:
   void Unlock();
 
 private:
+  ~VolatileBuffer();
+
+  /**
+   * Protects mLockCount, mFirstLock, and changes to the volatility of our
+   * buffer.  Other member variables are read-only except in Init() and the
+   * destructor.
+   */
+  Mutex mMutex;
+
   void* mBuf;
   size_t mSize;
   int mLockCount;

memory/volatile/VolatileBufferAshmem.cpp

@@ -22,7 +22,8 @@ extern "C" int posix_memalign(void** memptr, size_t alignment, size_t size);
 namespace mozilla {
 
 VolatileBuffer::VolatileBuffer()
-  : mBuf(nullptr)
+  : mMutex("VolatileBuffer")
+  , mBuf(nullptr)
   , mSize(0)
   , mLockCount(0)
   , mFd(-1)
@@ -72,6 +73,8 @@ heap_alloc:
 
 VolatileBuffer::~VolatileBuffer()
 {
+  MOZ_ASSERT(mLockCount == 0, "Being destroyed with non-zero lock count?");
+
   if (OnHeap()) {
     free(mBuf);
   } else {
@@ -83,6 +86,8 @@ VolatileBuffer::~VolatileBuffer()
 bool
 VolatileBuffer::Lock(void** aBuf)
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mBuf, "Attempting to lock an uninitialized VolatileBuffer");
 
   *aBuf = mBuf;
@@ -98,6 +103,8 @@ VolatileBuffer::Lock(void** aBuf)
 void
 VolatileBuffer::Unlock()
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mLockCount > 0, "VolatileBuffer unlocked too many times!");
   if (--mLockCount || OnHeap()) {
     return;

memory/volatile/VolatileBufferFallback.cpp

@@ -13,7 +13,8 @@ int posix_memalign(void** memptr, size_t alignment, size_t size);
 namespace mozilla {
 
 VolatileBuffer::VolatileBuffer()
-  : mBuf(nullptr)
+  : mMutex("VolatileBuffer")
+  , mBuf(nullptr)
   , mSize(0)
   , mLockCount(0)
 {
@@ -42,12 +43,16 @@ bool VolatileBuffer::Init(size_t aSize, size_t aAlignment)
 
 VolatileBuffer::~VolatileBuffer()
 {
+  MOZ_ASSERT(mLockCount == 0, "Being destroyed with non-zero lock count?");
+
   free(mBuf);
 }
 
 bool
 VolatileBuffer::Lock(void** aBuf)
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mBuf, "Attempting to lock an uninitialized VolatileBuffer");
 
   *aBuf = mBuf;
@@ -59,6 +64,8 @@ VolatileBuffer::Lock(void** aBuf)
 void
 VolatileBuffer::Unlock()
 {
+  MutexAutoLock lock(mMutex);
+
   mLockCount--;
   MOZ_ASSERT(mLockCount >= 0, "VolatileBuffer unlocked too many times!");
 }

memory/volatile/VolatileBufferOSX.cpp

@@ -16,7 +16,8 @@
 namespace mozilla {
 
 VolatileBuffer::VolatileBuffer()
-  : mBuf(nullptr)
+  : mMutex("VolatileBuffer")
+  , mBuf(nullptr)
   , mSize(0)
   , mLockCount(0)
   , mHeap(false)
@@ -53,6 +54,8 @@ heap_alloc:
 
 VolatileBuffer::~VolatileBuffer()
 {
+  MOZ_ASSERT(mLockCount == 0, "Being destroyed with non-zero lock count?");
+
   if (OnHeap()) {
     free(mBuf);
   } else {
@@ -63,6 +66,8 @@ VolatileBuffer::~VolatileBuffer()
 bool
 VolatileBuffer::Lock(void** aBuf)
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mBuf, "Attempting to lock an uninitialized VolatileBuffer");
 
   *aBuf = mBuf;
@@ -82,6 +87,8 @@ VolatileBuffer::Lock(void** aBuf)
 void
 VolatileBuffer::Unlock()
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mLockCount > 0, "VolatileBuffer unlocked too many times!");
   if (--mLockCount || OnHeap()) {
     return;

memory/volatile/VolatileBufferWindows.cpp

@@ -22,7 +22,8 @@ extern "C" int posix_memalign(void** memptr, size_t alignment, size_t size);
 namespace mozilla {
 
 VolatileBuffer::VolatileBuffer()
-  : mBuf(nullptr)
+  : mMutex("VolatileBuffer")
+  , mBuf(nullptr)
   , mSize(0)
   , mLockCount(0)
   , mHeap(false)
@@ -68,6 +69,8 @@ heap_alloc:
 
 VolatileBuffer::~VolatileBuffer()
 {
+  MOZ_ASSERT(mLockCount == 0, "Being destroyed with non-zero lock count?");
+
   if (OnHeap()) {
 #ifdef MOZ_MEMORY
     free(mBuf);
@@ -82,6 +85,8 @@ VolatileBuffer::~VolatileBuffer()
 bool
 VolatileBuffer::Lock(void** aBuf)
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mBuf, "Attempting to lock an uninitialized VolatileBuffer");
 
   *aBuf = mBuf;
@@ -107,6 +112,8 @@ VolatileBuffer::Lock(void** aBuf)
 void
 VolatileBuffer::Unlock()
 {
+  MutexAutoLock lock(mMutex);
+
   MOZ_ASSERT(mLockCount > 0, "VolatileBuffer unlocked too many times!");
   if (--mLockCount || OnHeap()) {
     return;