d4cb489434
This is a backward compatible implementation of compile time constructed String16 support. As much as we'd like a regular constexpr constructor for String16, we want to make sure the regular non-static String16 does not regress. We also need to make sure prebuilts built with previous version of String16 still works with new libutils. This means we cannot change the size of String16 objects and we cannot make anything virtual. To add a flag to indicate whether a String16 is static without increasing the size of non-static String16 objects, we repurpose a reserved field in SharedBuffer as "for client use". With this, we can tag every String16 and perform memory operation differently based on how the underlying buffers are allocated. By using StaticString16, we are able to eliminate the runtime construction of a String16 and move it out of .bss section. Bug: 138856262 Test: Run newly added unit tests. Change-Id: I72bb8dc27a59b9ef34e0d934bc1e00b0f675855a
140 lines
3.9 KiB
C++
140 lines
3.9 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 LOG_TAG "sharedbuffer"
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#include "SharedBuffer.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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// ---------------------------------------------------------------------------
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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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sb->mClientMetadata = 0;
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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 != nullptr) {
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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 nullptr;
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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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