1 files changed, 468 insertions, 0 deletions
diff --git a/media/libcubeb/src/cubeb_ringbuffer.h b/media/libcubeb/src/cubeb_ringbuffer.h
new file mode 100644
index 0000000000..f020351566
--- /dev/null
+++ b/media/libcubeb/src/cubeb_ringbuffer.h
@@ -0,0 +1,468 @@
+/*
+ * Copyright © 2016 Mozilla Foundation
+ *
+ * This program is made available under an ISC-style license.  See the
+ * accompanying file LICENSE for details.
+ */
+
+#ifndef CUBEB_RING_BUFFER_H
+#define CUBEB_RING_BUFFER_H
+
+#include "cubeb_utils.h"
+#include <algorithm>
+#include <atomic>
+#include <cstdint>
+#include <memory>
+#include <thread>
+
+/**
+ * Single producer single consumer lock-free and wait-free ring buffer.
+ *
+ * This data structure allows producing data from one thread, and consuming it
+ * on another thread, safely and without explicit synchronization. If used on
+ * two threads, this data structure uses atomics for thread safety. It is
+ * possible to disable the use of atomics at compile time and only use this data
+ * structure on one thread.
+ *
+ * The role for the producer and the consumer must be constant, i.e., the
+ * producer should always be on one thread and the consumer should always be on
+ * another thread.
+ *
+ * Some words about the inner workings of this class:
+ * - Capacity is fixed. Only one allocation is performed, in the constructor.
+ *   When reading and writing, the return value of the method allows checking if
+ *   the ring buffer is empty or full.
+ * - We always keep the read index at least one element ahead of the write
+ *   index, so we can distinguish between an empty and a full ring buffer: an
+ *   empty ring buffer is when the write index is at the same position as the
+ *   read index. A full buffer is when the write index is exactly one position
+ *   before the read index.
+ * - We synchronize updates to the read index after having read the data, and
+ *   the write index after having written the data. This means that the each
+ *   thread can only touch a portion of the buffer that is not touched by the
+ *   other thread.
+ * - Callers are expected to provide buffers. When writing to the queue,
+ *   elements are copied into the internal storage from the buffer passed in.
+ *   When reading from the queue, the user is expected to provide a buffer.
+ *   Because this is a ring buffer, data might not be contiguous in memory,
+ *   providing an external buffer to copy into is an easy way to have linear
+ *   data for further processing.
+ */
+template <typename T> class ring_buffer_base {
+public:
+  /**
+   * Constructor for a ring buffer.
+   *
+   * This performs an allocation, but is the only allocation that will happen
+   * for the life time of a `ring_buffer_base`.
+   *
+   * @param capacity The maximum number of element this ring buffer will hold.
+   */
+  ring_buffer_base(int capacity)
+      /* One more element to distinguish from empty and full buffer. */
+      : capacity_(capacity + 1)
+  {
+    assert(storage_capacity() < std::numeric_limits<int>::max() / 2 &&
+           "buffer too large for the type of index used.");
+    assert(capacity_ > 0);
+
+    data_.reset(new T[storage_capacity()]);
+    /* If this queue is using atomics, initializing those members as the last
+     * action in the constructor acts as a full barrier, and allow capacity() to
+     * be thread-safe. */
+    write_index_ = 0;
+    read_index_ = 0;
+  }
+  /**
+   * Push `count` zero or default constructed elements in the array.
+   *
+   * Only safely called on the producer thread.
+   *
+   * @param count The number of elements to enqueue.
+   * @return The number of element enqueued.
+   */
+  int enqueue_default(int count) { return enqueue(nullptr, count); }
+  /**
+   * @brief Put an element in the queue
+   *
+   * Only safely called on the producer thread.
+   *
+   * @param element The element to put in the queue.
+   *
+   * @return 1 if the element was inserted, 0 otherwise.
+   */
+  int enqueue(T & element) { return enqueue(&element, 1); }
+  /**
+   * Push `count` elements in the ring buffer.
+   *
+   * Only safely called on the producer thread.
+   *
+   * @param elements a pointer to a buffer containing at least `count` elements.
+   * If `elements` is nullptr, zero or default constructed elements are
+   * enqueued.
+   * @param count The number of elements to read from `elements`
+   * @return The number of elements successfully coped from `elements` and
+   * inserted into the ring buffer.
+   */
+  int enqueue(T * elements, int count)
+  {
+#ifndef NDEBUG
+    assert_correct_thread(producer_id);
+#endif
+
+    int wr_idx = write_index_.load(std::memory_order_relaxed);
+    int rd_idx = read_index_.load(std::memory_order_acquire);
+
+    if (full_internal(rd_idx, wr_idx)) {
+      return 0;
+    }
+
+    int to_write = std::min(available_write_internal(rd_idx, wr_idx), count);
+
+    /* First part, from the write index to the end of the array. */
+    int first_part = std::min(storage_capacity() - wr_idx, to_write);
+    /* Second part, from the beginning of the array */
+    int second_part = to_write - first_part;
+
+    if (elements) {
+      Copy(data_.get() + wr_idx, elements, first_part);
+      Copy(data_.get(), elements + first_part, second_part);
+    } else {
+      ConstructDefault(data_.get() + wr_idx, first_part);
+      ConstructDefault(data_.get(), second_part);
+    }
+
+    write_index_.store(increment_index(wr_idx, to_write),
+                       std::memory_order_release);
+
+    return to_write;
+  }
+  /**
+   * Retrieve at most `count` elements from the ring buffer, and copy them to
+   * `elements`, if non-null.
+   *
+   * Only safely called on the consumer side.
+   *
+   * @param elements A pointer to a buffer with space for at least `count`
+   * elements. If `elements` is `nullptr`, `count` element will be discarded.
+   * @param count The maximum number of elements to dequeue.
+   * @return The number of elements written to `elements`.
+   */
+  int dequeue(T * elements, int count)
+  {
+#ifndef NDEBUG
+    assert_correct_thread(consumer_id);
+#endif
+
+    int rd_idx = read_index_.load(std::memory_order_relaxed);
+    int wr_idx = write_index_.load(std::memory_order_acquire);
+
+    if (empty_internal(rd_idx, wr_idx)) {
+      return 0;
+    }
+
+    int to_read = std::min(available_read_internal(rd_idx, wr_idx), count);
+
+    int first_part = std::min(storage_capacity() - rd_idx, to_read);
+    int second_part = to_read - first_part;
+
+    if (elements) {
+      Copy(elements, data_.get() + rd_idx, first_part);
+      Copy(elements + first_part, data_.get(), second_part);
+    }
+
+    read_index_.store(increment_index(rd_idx, to_read),
+                      std::memory_order_release);
+
+    return to_read;
+  }
+  /**
+   * Get the number of available element for consuming.
+   *
+   * Only safely called on the consumer thread.
+   *
+   * @return The number of available elements for reading.
+   */
+  int available_read() const
+  {
+#ifndef NDEBUG
+    assert_correct_thread(consumer_id);
+#endif
+    return available_read_internal(
+        read_index_.load(std::memory_order_relaxed),
+        write_index_.load(std::memory_order_acquire));
+  }
+  /**
+   * Get the number of available elements for consuming.
+   *
+   * Only safely called on the producer thread.
+   *
+   * @return The number of empty slots in the buffer, available for writing.
+   */
+  int available_write() const
+  {
+#ifndef NDEBUG
+    assert_correct_thread(producer_id);
+#endif
+    return available_write_internal(
+        read_index_.load(std::memory_order_acquire),
+        write_index_.load(std::memory_order_relaxed));
+  }
+  /**
+   * Get the total capacity, for this ring buffer.
+   *
+   * Can be called safely on any thread.
+   *
+   * @return The maximum capacity of this ring buffer.
+   */
+  int capacity() const { return storage_capacity() - 1; }
+  /**
+   * Reset the consumer and producer thread identifier, in case the thread are
+   * being changed. This has to be externally synchronized. This is no-op when
+   * asserts are disabled.
+   */
+  void reset_thread_ids()
+  {
+#ifndef NDEBUG
+    consumer_id = producer_id = std::thread::id();
+#endif
+  }
+
+private:
+  /** Return true if the ring buffer is empty.
+   *
+   * @param read_index the read index to consider
+   * @param write_index the write index to consider
+   * @return true if the ring buffer is empty, false otherwise.
+   **/
+  bool empty_internal(int read_index, int write_index) const
+  {
+    return write_index == read_index;
+  }
+  /** Return true if the ring buffer is full.
+   *
+   * This happens if the write index is exactly one element behind the read
+   * index.
+   *
+   * @param read_index the read index to consider
+   * @param write_index the write index to consider
+   * @return true if the ring buffer is full, false otherwise.
+   **/
+  bool full_internal(int read_index, int write_index) const
+  {
+    return (write_index + 1) % storage_capacity() == read_index;
+  }
+  /**
+   * Return the size of the storage. It is one more than the number of elements
+   * that can be stored in the buffer.
+   *
+   * @return the number of elements that can be stored in the buffer.
+   */
+  int storage_capacity() const { return capacity_; }
+  /**
+   * Returns the number of elements available for reading.
+   *
+   * @return the number of available elements for reading.
+   */
+  int available_read_internal(int read_index, int write_index) const
+  {
+    if (write_index >= read_index) {
+      return write_index - read_index;
+    } else {
+      return write_index + storage_capacity() - read_index;
+    }
+  }
+  /**
+   * Returns the number of empty elements, available for writing.
+   *
+   * @return the number of elements that can be written into the array.
+   */
+  int available_write_internal(int read_index, int write_index) const
+  {
+    /* We substract one element here to always keep at least one sample
+     * free in the buffer, to distinguish between full and empty array. */
+    int rv = read_index - write_index - 1;
+    if (write_index >= read_index) {
+      rv += storage_capacity();
+    }
+    return rv;
+  }
+  /**
+   * Increments an index, wrapping it around the storage.
+   *
+   * @param index a reference to the index to increment.
+   * @param increment the number by which `index` is incremented.
+   * @return the new index.
+   */
+  int increment_index(int index, int increment) const
+  {
+    assert(increment >= 0);
+    return (index + increment) % storage_capacity();
+  }
+  /**
+   * @brief This allows checking that enqueue (resp. dequeue) are always called
+   * by the right thread.
+   *
+   * @param id the id of the thread that has called the calling method first.
+   */
+#ifndef NDEBUG
+  static void assert_correct_thread(std::thread::id & id)
+  {
+    if (id == std::thread::id()) {
+      id = std::this_thread::get_id();
+      return;
+    }
+    assert(id == std::this_thread::get_id());
+  }
+#endif
+  /** Index at which the oldest element is at, in samples. */
+  std::atomic<int> read_index_;
+  /** Index at which to write new elements. `write_index` is always at
+   * least one element ahead of `read_index_`. */
+  std::atomic<int> write_index_;
+  /** Maximum number of elements that can be stored in the ring buffer. */
+  const int capacity_;
+  /** Data storage */
+  std::unique_ptr<T[]> data_;
+#ifndef NDEBUG
+  /** The id of the only thread that is allowed to read from the queue. */
+  mutable std::thread::id consumer_id;
+  /** The id of the only thread that is allowed to write from the queue. */
+  mutable std::thread::id producer_id;
+#endif
+};
+
+/**
+ * Adapter for `ring_buffer_base` that exposes an interface in frames.
+ */
+template <typename T> class audio_ring_buffer_base {
+public:
+  /**
+   * @brief Constructor.
+   *
+   * @param channel_count       Number of channels.
+   * @param capacity_in_frames  The capacity in frames.
+   */
+  audio_ring_buffer_base(int channel_count, int capacity_in_frames)
+      : channel_count(channel_count),
+        ring_buffer(frames_to_samples(capacity_in_frames))
+  {
+    assert(channel_count > 0);
+  }
+  /**
+   * @brief Enqueue silence.
+   *
+   * Only safely called on the producer thread.
+   *
+   * @param frame_count The number of frames of silence to enqueue.
+   * @return  The number of frames of silence actually written to the queue.
+   */
+  int enqueue_default(int frame_count)
+  {
+    return samples_to_frames(
+        ring_buffer.enqueue(nullptr, frames_to_samples(frame_count)));
+  }
+  /**
+   * @brief Enqueue `frames_count` frames of audio.
+   *
+   * Only safely called from the producer thread.
+   *
+   * @param [in] frames If non-null, the frames to enqueue.
+   *                    Otherwise, silent frames are enqueued.
+   * @param frame_count The number of frames to enqueue.
+   *
+   * @return The number of frames enqueued
+   */
+
+  int enqueue(T * frames, int frame_count)
+  {
+    return samples_to_frames(
+        ring_buffer.enqueue(frames, frames_to_samples(frame_count)));
+  }
+
+  /**
+   * @brief Removes `frame_count` frames from the buffer, and
+   *        write them to `frames` if it is non-null.
+   *
+   * Only safely called on the consumer thread.
+   *
+   * @param frames      If non-null, the frames are copied to `frames`.
+   *                    Otherwise, they are dropped.
+   * @param frame_count The number of frames to remove.
+   *
+   * @return  The number of frames actually dequeud.
+   */
+  int dequeue(T * frames, int frame_count)
+  {
+    return samples_to_frames(
+        ring_buffer.dequeue(frames, frames_to_samples(frame_count)));
+  }
+  /**
+   * Get the number of available frames of audio for consuming.
+   *
+   * Only safely called on the consumer thread.
+   *
+   * @return The number of available frames of audio for reading.
+   */
+  int available_read() const
+  {
+    return samples_to_frames(ring_buffer.available_read());
+  }
+  /**
+   * Get the number of available frames of audio for consuming.
+   *
+   * Only safely called on the producer thread.
+   *
+   * @return The number of empty slots in the buffer, available for writing.
+   */
+  int available_write() const
+  {
+    return samples_to_frames(ring_buffer.available_write());
+  }
+  /**
+   * Get the total capacity, for this ring buffer.
+   *
+   * Can be called safely on any thread.
+   *
+   * @return The maximum capacity of this ring buffer.
+   */
+  int capacity() const { return samples_to_frames(ring_buffer.capacity()); }
+
+private:
+  /**
+   * @brief Frames to samples conversion.
+   *
+   * @param frames The number of frames.
+   *
+   * @return  A number of samples.
+   */
+  int frames_to_samples(int frames) const { return frames * channel_count; }
+  /**
+   * @brief Samples to frames conversion.
+   *
+   * @param samples The number of samples.
+   *
+   * @return  A number of frames.
+   */
+  int samples_to_frames(int samples) const { return samples / channel_count; }
+  /** Number of channels of audio that will stream through this ring buffer. */
+  int channel_count;
+  /** The underlying ring buffer that is used to store the data. */
+  ring_buffer_base<T> ring_buffer;
+};
+
+/**
+ * Lock-free instantiation of the `ring_buffer_base` type. This is safe to use
+ * from two threads, one producer, one consumer (that never change role),
+ * without explicit synchronization.
+ */
+template <typename T> using lock_free_queue = ring_buffer_base<T>;
+/**
+ * Lock-free instantiation of the `audio_ring_buffer` type. This is safe to use
+ * from two threads, one producer, one consumer (that never change role),
+ * without explicit synchronization.
+ */
+template <typename T>
+using lock_free_audio_ring_buffer = audio_ring_buffer_base<T>;
+
+#endif // CUBEB_RING_BUFFER_H