3e4c076ef2
Add comment that SharedBuffer is deprecated. Both aref and SharedBuffer had memory ordering bugs. Aref has no clients. SharedBuffer had several bugs, which are fixed here: mRefs was declared neither volatile, not atomic, allowing the compiler to, for example, reuse a stale previously loaded value. It used the default android_atomic release memory ordering, which is insufficient for reference count decrements. It used an ordinary memory read in onlyOwner() to check whether an object is safe to deallocate, without any attempt to ensure memory ordering. Comments claimed that SharedBuffer was exactly 16 bytes, but this was neither checked, nor correct on 64-bit platforms. This turns mRef into a std::atomic and removes the android_atomic dependency. Bug: 28826227 Change-Id: I39fa0b4f70ac0471b14ad274806fc4e0c0802e78
128 lines
3.5 KiB
C++
128 lines
3.5 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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#define __STDC_LIMIT_MACROS
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#include <stdint.h>
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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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int32_t prev = 1;
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if (onlyOwner() || ((prev = mRefs.fetch_sub(1, std::memory_order_release) == 1)
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&& (atomic_thread_fence(std::memory_order_acquire), true))) {
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mRefs.store(0, std::memory_order_relaxed);
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if ((flags & eKeepStorage) == 0) {
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free(const_cast<SharedBuffer*>(this));
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}
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}
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return prev;
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}
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}; // namespace android
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