Adds a modified copy of talk/base to webrtc/base. It is the first step in
migrating talk/base to webrtc/base.
BUG=N/A
R=niklas.enbom@webrtc.org
Review URL: https://webrtc-codereview.appspot.com/17479005
git-svn-id: http://webrtc.googlecode.com/svn/trunk@6129 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/base/atomicops.h b/webrtc/base/atomicops.h
new file mode 100644
index 0000000..6096e8c
--- /dev/null
+++ b/webrtc/base/atomicops.h
@@ -0,0 +1,149 @@
+/*
+ * Copyright 2011 The WebRTC Project Authors. All rights reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_ATOMICOPS_H_
+#define WEBRTC_BASE_ATOMICOPS_H_
+
+#include <string>
+
+#include "webrtc/base/basictypes.h"
+#include "webrtc/base/common.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/base/scoped_ptr.h"
+
+namespace rtc {
+
+// A single-producer, single-consumer, fixed-size queue.
+// All methods not ending in Unsafe can be safely called without locking,
+// provided that calls to consumer methods (Peek/Pop) or producer methods (Push)
+// only happen on a single thread per method type. If multiple threads need to
+// read simultaneously or write simultaneously, other synchronization is
+// necessary. Synchronization is also required if a call into any Unsafe method
+// could happen at the same time as a call to any other method.
+template <typename T>
+class FixedSizeLockFreeQueue {
+ private:
+// Atomic primitives and memory barrier
+#if defined(__arm__)
+ typedef uint32 Atomic32;
+
+ // Copied from google3/base/atomicops-internals-arm-v6plus.h
+ static inline void MemoryBarrier() {
+ asm volatile("dmb":::"memory");
+ }
+
+ // Adapted from google3/base/atomicops-internals-arm-v6plus.h
+ static inline void AtomicIncrement(volatile Atomic32* ptr) {
+ Atomic32 str_success, value;
+ asm volatile (
+ "1:\n"
+ "ldrex %1, [%2]\n"
+ "add %1, %1, #1\n"
+ "strex %0, %1, [%2]\n"
+ "teq %0, #0\n"
+ "bne 1b"
+ : "=&r"(str_success), "=&r"(value)
+ : "r" (ptr)
+ : "cc", "memory");
+ }
+#elif !defined(SKIP_ATOMIC_CHECK)
+#error "No atomic operations defined for the given architecture."
+#endif
+
+ public:
+ // Constructs an empty queue, with capacity 0.
+ FixedSizeLockFreeQueue() : pushed_count_(0),
+ popped_count_(0),
+ capacity_(0),
+ data_() {}
+ // Constructs an empty queue with the given capacity.
+ FixedSizeLockFreeQueue(size_t capacity) : pushed_count_(0),
+ popped_count_(0),
+ capacity_(capacity),
+ data_(new T[capacity]) {}
+
+ // Pushes a value onto the queue. Returns true if the value was successfully
+ // pushed (there was space in the queue). This method can be safely called at
+ // the same time as PeekFront/PopFront.
+ bool PushBack(T value) {
+ if (capacity_ == 0) {
+ LOG(LS_WARNING) << "Queue capacity is 0.";
+ return false;
+ }
+ if (IsFull()) {
+ return false;
+ }
+
+ data_[pushed_count_ % capacity_] = value;
+ // Make sure the data is written before the count is incremented, so other
+ // threads can't see the value exists before being able to read it.
+ MemoryBarrier();
+ AtomicIncrement(&pushed_count_);
+ return true;
+ }
+
+ // Retrieves the oldest value pushed onto the queue. Returns true if there was
+ // an item to peek (the queue was non-empty). This method can be safely called
+ // at the same time as PushBack.
+ bool PeekFront(T* value_out) {
+ if (capacity_ == 0) {
+ LOG(LS_WARNING) << "Queue capacity is 0.";
+ return false;
+ }
+ if (IsEmpty()) {
+ return false;
+ }
+
+ *value_out = data_[popped_count_ % capacity_];
+ return true;
+ }
+
+ // Retrieves the oldest value pushed onto the queue and removes it from the
+ // queue. Returns true if there was an item to pop (the queue was non-empty).
+ // This method can be safely called at the same time as PushBack.
+ bool PopFront(T* value_out) {
+ if (PeekFront(value_out)) {
+ AtomicIncrement(&popped_count_);
+ return true;
+ }
+ return false;
+ }
+
+ // Clears the current items in the queue and sets the new (fixed) size. This
+ // method cannot be called at the same time as any other method.
+ void ClearAndResizeUnsafe(int new_capacity) {
+ capacity_ = new_capacity;
+ data_.reset(new T[new_capacity]);
+ pushed_count_ = 0;
+ popped_count_ = 0;
+ }
+
+ // Returns true if there is no space left in the queue for new elements.
+ int IsFull() const { return pushed_count_ == popped_count_ + capacity_; }
+ // Returns true if there are no elements in the queue.
+ int IsEmpty() const { return pushed_count_ == popped_count_; }
+ // Returns the current number of elements in the queue. This is always in the
+ // range [0, capacity]
+ size_t Size() const { return pushed_count_ - popped_count_; }
+
+ // Returns the capacity of the queue (max size).
+ size_t capacity() const { return capacity_; }
+
+ private:
+ volatile Atomic32 pushed_count_;
+ volatile Atomic32 popped_count_;
+ size_t capacity_;
+ rtc::scoped_ptr<T[]> data_;
+ DISALLOW_COPY_AND_ASSIGN(FixedSizeLockFreeQueue);
+};
+
+}
+
+#endif // WEBRTC_BASE_ATOMICOPS_H_