gfxBaseSharedMemorySurface.h

// vim:set ts=4 sts=2 sw=2 et cin:
/* -*- Mode: C++; tab-width: 20; 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/. */

#ifndef GFX_SHARED_MEMORYSURFACE_H
#define GFX_SHARED_MEMORYSURFACE_H

#include "mozilla/gfx/2D.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;

 protected:
  virtual ~gfxBaseSharedMemorySurface() {
    MOZ_COUNT_DTOR(gfxBaseSharedMemorySurface);
  }

 public:
  /**
   * 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 mozilla::gfx::IntSize& 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);
    mozilla::gfx::IntSize size(shmInfo->width, shmInfo->height);
    if (!mozilla::gfx::Factory::CheckSurfaceSize(size)) return nullptr;

    gfxImageFormat format = shmInfo->format;
    long stride = gfxImageSurface::ComputeStride(size, format);

    RefPtr<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 mozilla::gfx::IntSize& 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 mozilla::gfx::IntSize& 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 mozilla::gfx::IntSize& 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 mozilla::gfx::IntSize& aSize,
                                      gfxImageFormat aFormat,
                                      SharedMemory::SharedMemoryType aShmType) {
    if (!mozilla::gfx::Factory::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;
    }

    RefPtr<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 */