476dbc48da
We refactor this mildly in the hopes of making this a little easier to follow for future readers. We also go through the dealloc() method so if we decide to invoke the SharedBuffer destructor in the future, we only need to remember it in one place. In addition, this is slightly more efficient in the multi-owner case, since we no longer subtract to 0 and then (redundantly) set the reference count explicitly to 0 as well. Change-Id: Ifc773bd7900c89c36ac24904b2716f02cb57c095
137 lines
3.8 KiB
C++
137 lines
3.8 KiB
C++
/*
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* Copyright (C) 2005 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <stdlib.h>
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#include <string.h>
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#include <log/log.h>
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#include "SharedBuffer.h"
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// ---------------------------------------------------------------------------
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namespace android {
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SharedBuffer* SharedBuffer::alloc(size_t size)
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{
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// Don't overflow if the combined size of the buffer / header is larger than
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// size_max.
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LOG_ALWAYS_FATAL_IF((size >= (SIZE_MAX - sizeof(SharedBuffer))),
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"Invalid buffer size %zu", size);
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SharedBuffer* sb = static_cast<SharedBuffer *>(malloc(sizeof(SharedBuffer) + size));
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if (sb) {
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// Should be std::atomic_init(&sb->mRefs, 1);
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// But that generates a warning with some compilers.
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// The following is OK on Android-supported platforms.
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sb->mRefs.store(1, std::memory_order_relaxed);
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sb->mSize = size;
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}
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return sb;
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}
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void SharedBuffer::dealloc(const SharedBuffer* released)
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{
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free(const_cast<SharedBuffer*>(released));
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}
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SharedBuffer* SharedBuffer::edit() const
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{
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if (onlyOwner()) {
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return const_cast<SharedBuffer*>(this);
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}
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SharedBuffer* sb = alloc(mSize);
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if (sb) {
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memcpy(sb->data(), data(), size());
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release();
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}
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return sb;
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}
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SharedBuffer* SharedBuffer::editResize(size_t newSize) const
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{
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if (onlyOwner()) {
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SharedBuffer* buf = const_cast<SharedBuffer*>(this);
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if (buf->mSize == newSize) return buf;
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// Don't overflow if the combined size of the new buffer / header is larger than
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// size_max.
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LOG_ALWAYS_FATAL_IF((newSize >= (SIZE_MAX - sizeof(SharedBuffer))),
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"Invalid buffer size %zu", newSize);
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buf = (SharedBuffer*)realloc(buf, sizeof(SharedBuffer) + newSize);
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if (buf != NULL) {
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buf->mSize = newSize;
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return buf;
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}
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}
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SharedBuffer* sb = alloc(newSize);
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if (sb) {
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const size_t mySize = mSize;
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memcpy(sb->data(), data(), newSize < mySize ? newSize : mySize);
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release();
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}
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return sb;
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}
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SharedBuffer* SharedBuffer::attemptEdit() const
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{
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if (onlyOwner()) {
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return const_cast<SharedBuffer*>(this);
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}
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return 0;
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}
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SharedBuffer* SharedBuffer::reset(size_t new_size) const
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{
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// cheap-o-reset.
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SharedBuffer* sb = alloc(new_size);
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if (sb) {
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release();
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}
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return sb;
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}
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void SharedBuffer::acquire() const {
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mRefs.fetch_add(1, std::memory_order_relaxed);
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}
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int32_t SharedBuffer::release(uint32_t flags) const
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{
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const bool useDealloc = ((flags & eKeepStorage) == 0);
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if (onlyOwner()) {
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// Since we're the only owner, our reference count goes to zero.
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mRefs.store(0, std::memory_order_relaxed);
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if (useDealloc) {
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dealloc(this);
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}
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// As the only owner, our previous reference count was 1.
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return 1;
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}
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// There's multiple owners, we need to use an atomic decrement.
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int32_t prevRefCount = mRefs.fetch_sub(1, std::memory_order_release);
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if (prevRefCount == 1) {
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// We're the last reference, we need the acquire fence.
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atomic_thread_fence(std::memory_order_acquire);
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if (useDealloc) {
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dealloc(this);
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}
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}
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return prevRefCount;
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}
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}; // namespace android
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