87 lines
2.6 KiB
C++
87 lines
2.6 KiB
C++
//===-- xray_buffer_queue.h ------------------------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file is a part of XRay, a dynamic runtime instrumentation system.
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//
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// Defines the interface for a buffer queue implementation.
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//
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//===----------------------------------------------------------------------===//
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#ifndef XRAY_BUFFER_QUEUE_H
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#define XRAY_BUFFER_QUEUE_H
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#include <atomic>
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#include <cstdint>
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#include <deque>
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#include <mutex>
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#include <system_error>
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#include <unordered_set>
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namespace __xray {
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/// BufferQueue implements a circular queue of fixed sized buffers (much like a
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/// freelist) but is concerned mostly with making it really quick to initialise,
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/// finalise, and get/return buffers to the queue. This is one key component of
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/// the "flight data recorder" (FDR) mode to support ongoing XRay function call
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/// trace collection.
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class BufferQueue {
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public:
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struct Buffer {
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void *Buffer = nullptr;
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std::size_t Size = 0;
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};
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private:
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std::size_t BufferSize;
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std::deque<Buffer> Buffers;
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std::mutex Mutex;
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std::unordered_set<void *> OwnedBuffers;
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std::atomic<bool> Finalizing;
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public:
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/// Initialise a queue of size |N| with buffers of size |B|.
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BufferQueue(std::size_t B, std::size_t N);
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/// Updates |Buf| to contain the pointer to an appropriate buffer. Returns an
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/// error in case there are no available buffers to return when we will run
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/// over the upper bound for the total buffers.
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///
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/// Requirements:
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/// - BufferQueue is not finalising.
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///
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/// Returns:
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/// - std::errc::not_enough_memory on exceeding MaxSize.
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/// - no error when we find a Buffer.
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/// - std::errc::state_not_recoverable on finalising BufferQueue.
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std::error_code getBuffer(Buffer &Buf);
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/// Updates |Buf| to point to nullptr, with size 0.
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///
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/// Returns:
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/// - ...
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std::error_code releaseBuffer(Buffer &Buf);
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bool finalizing() const { return Finalizing.load(std::memory_order_acquire); }
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// Sets the state of the BufferQueue to finalizing, which ensures that:
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//
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// - All subsequent attempts to retrieve a Buffer will fail.
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// - All releaseBuffer operations will not fail.
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//
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// After a call to finalize succeeds, all subsequent calls to finalize will
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// fail with std::errc::state_not_recoverable.
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std::error_code finalize();
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// Cleans up allocated buffers.
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~BufferQueue();
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};
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} // namespace __xray
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#endif // XRAY_BUFFER_QUEUE_H
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