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/*
* Copyright (C) 2005 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "sharedbuffer"
#include "SharedBuffer.h"
#include <stdlib.h>
#include <string.h>
#include <log/log.h>
// ---------------------------------------------------------------------------
namespace android {
SharedBuffer* SharedBuffer::alloc(size_t size)
{
// Don't overflow if the combined size of the buffer / header is larger than
// size_max.
LOG_ALWAYS_FATAL_IF((size >= (SIZE_MAX - sizeof(SharedBuffer))),
"Invalid buffer size %zu", size);
SharedBuffer* sb = static_cast<SharedBuffer *>(malloc(sizeof(SharedBuffer) + size));
if (sb) {
// Should be std::atomic_init(&sb->mRefs, 1);
// But that generates a warning with some compilers.
// The following is OK on Android-supported platforms.
sb->mRefs.store(1, std::memory_order_relaxed);
sb->mSize = size;
}
return sb;
}
void SharedBuffer::dealloc(const SharedBuffer* released)
{
free(const_cast<SharedBuffer*>(released));
}
SharedBuffer* SharedBuffer::edit() const
{
if (onlyOwner()) {
return const_cast<SharedBuffer*>(this);
}
SharedBuffer* sb = alloc(mSize);
if (sb) {
memcpy(sb->data(), data(), size());
release();
}
return sb;
}
SharedBuffer* SharedBuffer::editResize(size_t newSize) const
{
if (onlyOwner()) {
SharedBuffer* buf = const_cast<SharedBuffer*>(this);
if (buf->mSize == newSize) return buf;
// Don't overflow if the combined size of the new buffer / header is larger than
// size_max.
LOG_ALWAYS_FATAL_IF((newSize >= (SIZE_MAX - sizeof(SharedBuffer))),
"Invalid buffer size %zu", newSize);
buf = (SharedBuffer*)realloc(buf, sizeof(SharedBuffer) + newSize);
if (buf != NULL) {
buf->mSize = newSize;
return buf;
}
}
SharedBuffer* sb = alloc(newSize);
if (sb) {
const size_t mySize = mSize;
memcpy(sb->data(), data(), newSize < mySize ? newSize : mySize);
release();
}
return sb;
}
SharedBuffer* SharedBuffer::attemptEdit() const
{
if (onlyOwner()) {
return const_cast<SharedBuffer*>(this);
}
return 0;
}
SharedBuffer* SharedBuffer::reset(size_t new_size) const
{
// cheap-o-reset.
SharedBuffer* sb = alloc(new_size);
if (sb) {
release();
}
return sb;
}
void SharedBuffer::acquire() const {
mRefs.fetch_add(1, std::memory_order_relaxed);
}
int32_t SharedBuffer::release(uint32_t flags) const
{
const bool useDealloc = ((flags & eKeepStorage) == 0);
if (onlyOwner()) {
// Since we're the only owner, our reference count goes to zero.
mRefs.store(0, std::memory_order_relaxed);
if (useDealloc) {
dealloc(this);
}
// As the only owner, our previous reference count was 1.
return 1;
}
// There's multiple owners, we need to use an atomic decrement.
int32_t prevRefCount = mRefs.fetch_sub(1, std::memory_order_release);
if (prevRefCount == 1) {
// We're the last reference, we need the acquire fence.
atomic_thread_fence(std::memory_order_acquire);
if (useDealloc) {
dealloc(this);
}
}
return prevRefCount;
}
}; // namespace android
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