V8 Sampling Profiler: Collect V8 sample trace events on Linux and MacOS

content/renderer/devtools/lock_free_circular_queue.h

Index: content/renderer/devtools/lock_free_circular_queue.h
diff --git a/content/renderer/devtools/lock_free_circular_queue.h b/content/renderer/devtools/lock_free_circular_queue.h
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+++ b/content/renderer/devtools/lock_free_circular_queue.h
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_RENDERER_DEVTOOLS_LOCK_FREE_CIRCULAR_QUEUE_H_
+#define CONTENT_RENDERER_DEVTOOLS_LOCK_FREE_CIRCULAR_QUEUE_H_
+
+#include "base/atomicops.h"
+#include "base/memory/aligned_memory.h"
+
+#define CACHELINE_ALIGNED ALIGNAS(64)
+
+namespace content {
+
+MSVC_PUSH_DISABLE_WARNING(4324)  // structure was padded due to align
+
+// Lock-free cache-friendly sampling circular queue for large
+// records. Intended for fast transfer of large records between a
+// single producer and a single consumer. If the queue is full,
+// StartEnqueue will return nullptr. The queue is designed with
+// a goal in mind to evade cache lines thrashing by preventing
+// simultaneous reads and writes to adjanced memory locations.
+template <typename T, unsigned Length>
+class LockFreeCircularQueue {
+ public:
+  // Executed on the application thread.
+  LockFreeCircularQueue();
+  ~LockFreeCircularQueue();
+
+  // StartEnqueue returns a pointer to a memory location for storing the next
+  // record or nullptr if all entries are full at the moment.
+  T* StartEnqueue();
+  // Notifies the queue that the producer has complete writing data into the
+  // memory returned by StartEnqueue and it can be passed to the consumer.
+  void FinishEnqueue();
+
+  // Executed on the consumer (analyzer) thread.
+  // Retrieves, but does not remove, the head of this queue, returning nullptr
+  // if this queue is empty. After the record had been read by a consumer,
+  // Remove must be called.
+  T* Peek();
+  void Remove();
+
+  // The class fields have stricter alignment requirements than a normal new
+  // can fulfil, so we need to provide our own new/delete here.
+  void* operator new(size_t size);
+  void operator delete(void* ptr);
+
+ private:
+  // Reserved values for the entry marker.
+  enum {
+    kEmpty,  // Marks clean (processed) entries.
+    kFull    // Marks entries already filled by the producer but not yet
+             // completely processed by the consumer.
+  };
+
+  struct CACHELINE_ALIGNED Entry {
+    Entry() : marker(kEmpty) {}
+    T record;
+    base::subtle::Atomic32 marker;
+  };
+
+  Entry* Next(Entry* entry);
+
+  Entry buffer_[Length];
+  CACHELINE_ALIGNED Entry* enqueue_pos_;
+  CACHELINE_ALIGNED Entry* dequeue_pos_;
+
+  DISALLOW_COPY_AND_ASSIGN(LockFreeCircularQueue);
+};
+
+MSVC_POP_WARNING()
+
+template <typename T, unsigned L>
+LockFreeCircularQueue<T, L>::LockFreeCircularQueue()
+    : enqueue_pos_(buffer_), dequeue_pos_(buffer_) {
+}
+
+template <typename T, unsigned L>
+LockFreeCircularQueue<T, L>::~LockFreeCircularQueue() {
+}
+
+template <typename T, unsigned L>
+T* LockFreeCircularQueue<T, L>::Peek() {
+  base::subtle::MemoryBarrier();
+  if (base::subtle::Acquire_Load(&dequeue_pos_->marker) == kFull) {
+    return &dequeue_pos_->record;
+  }
+  return nullptr;
+}
+
+template <typename T, unsigned L>
+void LockFreeCircularQueue<T, L>::Remove() {
+  base::subtle::Release_Store(&dequeue_pos_->marker, kEmpty);
+  dequeue_pos_ = Next(dequeue_pos_);
+}
+
+template <typename T, unsigned L>
+T* LockFreeCircularQueue<T, L>::StartEnqueue() {
+  base::subtle::MemoryBarrier();
+  if (base::subtle::Acquire_Load(&enqueue_pos_->marker) == kEmpty) {
+    return &enqueue_pos_->record;
+  }
+  return nullptr;
+}
+
+template <typename T, unsigned L>
+void LockFreeCircularQueue<T, L>::FinishEnqueue() {
+  base::subtle::Release_Store(&enqueue_pos_->marker, kFull);
+  enqueue_pos_ = Next(enqueue_pos_);
+}
+
+template <typename T, unsigned L>
+typename LockFreeCircularQueue<T, L>::Entry* LockFreeCircularQueue<T, L>::Next(
+    Entry* entry) {
+  Entry* next = entry + 1;
+  if (next == &buffer_[L])
+    return buffer_;
+  return next;
+}
+
+template <typename T, unsigned L>
+void* LockFreeCircularQueue<T, L>::operator new(size_t size) {
+  typedef LockFreeCircularQueue<T, L> QueueTypeAlias;
+  return base::AlignedAlloc(size, ALIGNOF(QueueTypeAlias));
+}
+
+template <typename T, unsigned L>
+void LockFreeCircularQueue<T, L>::operator delete(void* ptr) {
+  base::AlignedFree(ptr);
+}
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_DEVTOOLS_LOCK_FREE_CIRCULAR_QUEUE_H_