
This patch has a partial implementation of provider and does not include any device motion fetchers. The patch features: - chromium-side event pump - shared memory reader and buffer representation - IPC messages and filters for shared memory communication - service class to keep track of listening renderers BUG=135804 Review URL: https://chromiumcodereview.appspot.com/14678012 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@211043 0039d316-1c4b-4281-b951-d872f2087c98
59 lines
1.9 KiB
C++
59 lines
1.9 KiB
C++
// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "shared_memory_seqlock_reader.h"
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namespace internal {
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SharedMemorySeqLockReaderBase::SharedMemorySeqLockReaderBase() { }
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SharedMemorySeqLockReaderBase::~SharedMemorySeqLockReaderBase() { }
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void*
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SharedMemorySeqLockReaderBase::InitializeSharedMemory(
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base::SharedMemoryHandle shared_memory_handle, size_t buffer_size) {
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renderer_shared_memory_handle_ = shared_memory_handle;
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if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
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return 0;
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renderer_shared_memory_.reset(new base::SharedMemory(
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renderer_shared_memory_handle_, true));
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return (renderer_shared_memory_->Map(buffer_size))
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? renderer_shared_memory_->memory()
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: 0;
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}
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bool SharedMemorySeqLockReaderBase::FetchFromBuffer(
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content::OneWriterSeqLock* seqlock, void* final, void* temp, void* from,
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size_t size) {
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if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
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return false;
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// Only try to read this many times before failing to avoid waiting here
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// very long in case of contention with the writer.
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int contention_count = -1;
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base::subtle::Atomic32 version;
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do {
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version = seqlock->ReadBegin();
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memcpy(temp, from, size);
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++contention_count;
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if (contention_count == kMaximumContentionCount)
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break;
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} while (seqlock->ReadRetry(version));
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if (contention_count >= kMaximumContentionCount) {
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// We failed to successfully read, presumably because the hardware
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// thread was taking unusually long. Don't copy the data to the output
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// buffer, and simply leave what was there before.
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return false;
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}
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// New data was read successfully, copy it into the output buffer.
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memcpy(final, temp, size);
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return true;
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}
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} // namespace internal
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