54828dc739
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
(cherry picked from commit 3e4c076ef2)
146 lines
4.5 KiB
C++
146 lines
4.5 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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/*
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* DEPRECATED. DO NOT USE FOR NEW CODE.
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*/
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#ifndef ANDROID_SHARED_BUFFER_H
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#define ANDROID_SHARED_BUFFER_H
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#include <atomic>
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#include <stdint.h>
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#include <sys/types.h>
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// ---------------------------------------------------------------------------
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namespace android {
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class SharedBuffer
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{
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public:
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/* flags to use with release() */
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enum {
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eKeepStorage = 0x00000001
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};
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/*! allocate a buffer of size 'size' and acquire() it.
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* call release() to free it.
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*/
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static SharedBuffer* alloc(size_t size);
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/*! free the memory associated with the SharedBuffer.
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* Fails if there are any users associated with this SharedBuffer.
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* In other words, the buffer must have been release by all its
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* users.
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*/
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static void dealloc(const SharedBuffer* released);
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//! access the data for read
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inline const void* data() const;
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//! access the data for read/write
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inline void* data();
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//! get size of the buffer
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inline size_t size() const;
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//! get back a SharedBuffer object from its data
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static inline SharedBuffer* bufferFromData(void* data);
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//! get back a SharedBuffer object from its data
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static inline const SharedBuffer* bufferFromData(const void* data);
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//! get the size of a SharedBuffer object from its data
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static inline size_t sizeFromData(const void* data);
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//! edit the buffer (get a writtable, or non-const, version of it)
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SharedBuffer* edit() const;
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//! edit the buffer, resizing if needed
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SharedBuffer* editResize(size_t size) const;
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//! like edit() but fails if a copy is required
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SharedBuffer* attemptEdit() const;
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//! resize and edit the buffer, loose it's content.
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SharedBuffer* reset(size_t size) const;
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//! acquire/release a reference on this buffer
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void acquire() const;
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/*! release a reference on this buffer, with the option of not
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* freeing the memory associated with it if it was the last reference
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* returns the previous reference count
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*/
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int32_t release(uint32_t flags = 0) const;
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//! returns wether or not we're the only owner
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inline bool onlyOwner() const;
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private:
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inline SharedBuffer() { }
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inline ~SharedBuffer() { }
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SharedBuffer(const SharedBuffer&);
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SharedBuffer& operator = (const SharedBuffer&);
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// Must be sized to preserve correct alignment.
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mutable std::atomic<int32_t> mRefs;
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size_t mSize;
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uint32_t mReserved[2];
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};
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static_assert(sizeof(SharedBuffer) % 8 == 0
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&& (sizeof(size_t) > 4 || sizeof(SharedBuffer) == 16),
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"SharedBuffer has unexpected size");
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// ---------------------------------------------------------------------------
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const void* SharedBuffer::data() const {
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return this + 1;
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}
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void* SharedBuffer::data() {
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return this + 1;
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}
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size_t SharedBuffer::size() const {
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return mSize;
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}
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SharedBuffer* SharedBuffer::bufferFromData(void* data) {
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return data ? static_cast<SharedBuffer *>(data)-1 : 0;
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}
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const SharedBuffer* SharedBuffer::bufferFromData(const void* data) {
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return data ? static_cast<const SharedBuffer *>(data)-1 : 0;
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}
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size_t SharedBuffer::sizeFromData(const void* data) {
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return data ? bufferFromData(data)->mSize : 0;
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}
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bool SharedBuffer::onlyOwner() const {
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return (mRefs.load(std::memory_order_acquire) == 1);
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}
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}; // namespace android
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// ---------------------------------------------------------------------------
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#endif // ANDROID_VECTOR_H
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