diff -r 000000000000 -r 6474c204b198 gfx/thebes/gfxBaseSharedMemorySurface.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/thebes/gfxBaseSharedMemorySurface.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,198 @@
+// vim:set ts=4 sts=4 sw=4 et cin:
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * 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/. */
+
+#ifndef GFX_SHARED_MEMORYSURFACE_H
+#define GFX_SHARED_MEMORYSURFACE_H
+
+#include "mozilla/ipc/Shmem.h"
+#include "mozilla/ipc/SharedMemory.h"
+
+#include "gfxASurface.h"
+#include "gfxImageSurface.h"
+#include "pratom.h"
+
+typedef struct _cairo_user_data_key cairo_user_data_key_t;
+
+struct SharedImageInfo {
+    int32_t width;
+    int32_t height;
+    gfxImageFormat format;
+    int32_t readCount;
+};
+
+inline SharedImageInfo*
+GetShmInfoPtr(const mozilla::ipc::Shmem& aShmem)
+{
+    return reinterpret_cast<SharedImageInfo*>
+        (aShmem.get<char>() + aShmem.Size<char>() - sizeof(SharedImageInfo));
+}
+
+extern const cairo_user_data_key_t SHM_KEY;
+
+template <typename Base, typename Sub>
+class gfxBaseSharedMemorySurface : public Base {
+    typedef mozilla::ipc::SharedMemory SharedMemory;
+    typedef mozilla::ipc::Shmem Shmem;
+    friend class gfxReusableSharedImageSurfaceWrapper;
+
+public:
+    virtual ~gfxBaseSharedMemorySurface()
+    {
+        MOZ_COUNT_DTOR(gfxBaseSharedMemorySurface);
+    }
+
+    /**
+     * Return a new gfxSharedImageSurface around a shmem segment newly
+     * allocated by this function.  |aAllocator| is the object used to
+     * allocate the new shmem segment.  Null is returned if creating
+     * the surface failed.
+     *
+     * NB: the *caller* is responsible for freeing the Shmem allocated
+     * by this function.
+     */
+    template<class ShmemAllocator>
+    static already_AddRefed<Sub>
+    Create(ShmemAllocator* aAllocator,
+           const gfxIntSize& aSize,
+           gfxImageFormat aFormat,
+           SharedMemory::SharedMemoryType aShmType = SharedMemory::TYPE_BASIC)
+    {
+        return Create<ShmemAllocator, false>(aAllocator, aSize, aFormat, aShmType);
+    }
+
+    /**
+     * Return a new gfxSharedImageSurface that wraps a shmem segment
+     * already created by the Create() above.  Bad things will happen
+     * if an attempt is made to wrap any other shmem segment.  Null is
+     * returned if creating the surface failed.
+     */
+    static already_AddRefed<Sub>
+    Open(const Shmem& aShmem)
+    {
+        SharedImageInfo* shmInfo = GetShmInfoPtr(aShmem);
+        gfxIntSize size(shmInfo->width, shmInfo->height);
+        if (!gfxASurface::CheckSurfaceSize(size))
+            return nullptr;
+       
+        gfxImageFormat format = (gfxImageFormat)shmInfo->format;
+        long stride = gfxImageSurface::ComputeStride(size, format);
+
+        nsRefPtr<Sub> s =
+            new Sub(size,
+                    stride,
+                    format,
+                    aShmem);
+        // We didn't create this Shmem and so don't free it on errors
+        return (s->CairoStatus() != 0) ? nullptr : s.forget();
+    }
+
+    template<class ShmemAllocator>
+    static already_AddRefed<Sub>
+    CreateUnsafe(ShmemAllocator* aAllocator,
+                 const gfxIntSize& aSize,
+                 gfxImageFormat aFormat,
+                 SharedMemory::SharedMemoryType aShmType = SharedMemory::TYPE_BASIC)
+    {
+        return Create<ShmemAllocator, true>(aAllocator, aSize, aFormat, aShmType);
+    }
+
+    Shmem& GetShmem() { return mShmem; }
+
+    static bool IsSharedImage(gfxASurface *aSurface)
+    {
+        return (aSurface
+                && aSurface->GetType() == gfxSurfaceType::Image
+                && aSurface->GetData(&SHM_KEY));
+    }
+
+protected:
+    gfxBaseSharedMemorySurface(const gfxIntSize& aSize, long aStride, 
+                               gfxImageFormat aFormat, 
+                               const Shmem& aShmem)
+      : Base(aShmem.get<unsigned char>(), aSize, aStride, aFormat)
+    {
+        MOZ_COUNT_CTOR(gfxBaseSharedMemorySurface);
+
+        mShmem = aShmem;
+        this->SetData(&SHM_KEY, this, nullptr);
+    }
+
+private:
+    void WriteShmemInfo()
+    {
+        SharedImageInfo* shmInfo = GetShmInfoPtr(mShmem);
+        shmInfo->width = this->mSize.width;
+        shmInfo->height = this->mSize.height;
+        shmInfo->format = this->mFormat;
+        shmInfo->readCount = 0;
+    }
+
+    int32_t
+    ReadLock()
+    {
+        SharedImageInfo* shmInfo = GetShmInfoPtr(mShmem);
+        return PR_ATOMIC_INCREMENT(&shmInfo->readCount);
+    }
+
+    int32_t
+    ReadUnlock()
+    {
+        SharedImageInfo* shmInfo = GetShmInfoPtr(mShmem);
+        return PR_ATOMIC_DECREMENT(&shmInfo->readCount);
+    }
+
+    int32_t
+    GetReadCount()
+    {
+        SharedImageInfo* shmInfo = GetShmInfoPtr(mShmem);
+        return shmInfo->readCount;
+    }
+
+    static size_t GetAlignedSize(const gfxIntSize& aSize, long aStride)
+    {
+        #define MOZ_ALIGN_WORD(x) (((x) + 3) & ~3)
+        return MOZ_ALIGN_WORD(sizeof(SharedImageInfo) + aSize.height * aStride);
+    }
+
+    template<class ShmemAllocator, bool Unsafe>
+    static already_AddRefed<Sub>
+    Create(ShmemAllocator* aAllocator,
+           const gfxIntSize& aSize,
+           gfxImageFormat aFormat,
+           SharedMemory::SharedMemoryType aShmType)
+    {
+        if (!gfxASurface::CheckSurfaceSize(aSize))
+            return nullptr;
+
+        Shmem shmem;
+        long stride = gfxImageSurface::ComputeStride(aSize, aFormat);
+        size_t size = GetAlignedSize(aSize, stride);
+        if (!Unsafe) {
+            if (!aAllocator->AllocShmem(size, aShmType, &shmem))
+                return nullptr;
+        } else {
+            if (!aAllocator->AllocUnsafeShmem(size, aShmType, &shmem))
+                return nullptr;
+        }
+
+        nsRefPtr<Sub> s =
+            new Sub(aSize, stride, aFormat, shmem);
+        if (s->CairoStatus() != 0) {
+            aAllocator->DeallocShmem(shmem);
+            return nullptr;
+        }
+        s->WriteShmemInfo();
+        return s.forget();
+    }
+
+    Shmem mShmem;
+
+    // Calling these is very bad, disallow it
+    gfxBaseSharedMemorySurface(const gfxBaseSharedMemorySurface&);
+    gfxBaseSharedMemorySurface& operator=(const gfxBaseSharedMemorySurface&);
+};
+
+#endif /* GFX_SHARED_MEMORYSURFACE_H */