1/*
2 * libjingle
3 * Copyright 2011, Google Inc.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 *
8 *  1. Redistributions of source code must retain the above copyright notice,
9 *     this list of conditions and the following disclaimer.
10 *  2. Redistributions in binary form must reproduce the above copyright notice,
11 *     this list of conditions and the following disclaimer in the documentation
12 *     and/or other materials provided with the distribution.
13 *  3. The name of the author may not be used to endorse or promote products
14 *     derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
17 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
18 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
19 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
21 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
22 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
23 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
25 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28#ifndef TALK_BASE_ATOMICOPS_H_
29#define TALK_BASE_ATOMICOPS_H_
30
31#include <string>
32
33#include "talk/base/basictypes.h"
34#include "talk/base/common.h"
35#include "talk/base/logging.h"
36#include "talk/base/scoped_ptr.h"
37
38namespace talk_base {
39
40// A single-producer, single-consumer, fixed-size queue.
41// All methods not ending in Unsafe can be safely called without locking,
42// provided that calls to consumer methods (Peek/Pop) or producer methods (Push)
43// only happen on a single thread per method type. If multiple threads need to
44// read simultaneously or write simultaneously, other synchronization is
45// necessary. Synchronization is also required if a call into any Unsafe method
46// could happen at the same time as a call to any other method.
47template <typename T>
48class FixedSizeLockFreeQueue {
49 private:
50// Atomic primitives and memory barrier
51#if defined(__arm__)
52  typedef uint32 Atomic32;
53
54  // Copied from google3/base/atomicops-internals-arm-v6plus.h
55  static inline void MemoryBarrier() {
56    asm volatile("dmb":::"memory");
57  }
58
59  // Adapted from google3/base/atomicops-internals-arm-v6plus.h
60  static inline void AtomicIncrement(volatile Atomic32* ptr) {
61    Atomic32 str_success, value;
62    asm volatile (
63        "1:\n"
64        "ldrex  %1, [%2]\n"
65        "add    %1, %1, #1\n"
66        "strex  %0, %1, [%2]\n"
67        "teq    %0, #0\n"
68        "bne    1b"
69        : "=&r"(str_success), "=&r"(value)
70        : "r" (ptr)
71        : "cc", "memory");
72  }
73#elif !defined(SKIP_ATOMIC_CHECK)
74#error "No atomic operations defined for the given architecture."
75#endif
76
77 public:
78  // Constructs an empty queue, with capacity 0.
79  FixedSizeLockFreeQueue() : pushed_count_(0),
80                             popped_count_(0),
81                             capacity_(0),
82                             data_() {}
83  // Constructs an empty queue with the given capacity.
84  FixedSizeLockFreeQueue(size_t capacity) : pushed_count_(0),
85                                            popped_count_(0),
86                                            capacity_(capacity),
87                                            data_(new T[capacity]) {}
88
89  // Pushes a value onto the queue. Returns true if the value was successfully
90  // pushed (there was space in the queue). This method can be safely called at
91  // the same time as PeekFront/PopFront.
92  bool PushBack(T value) {
93    if (capacity_ == 0) {
94      LOG(LS_WARNING) << "Queue capacity is 0.";
95      return false;
96    }
97    if (IsFull()) {
98      return false;
99    }
100
101    data_[pushed_count_ % capacity_] = value;
102    // Make sure the data is written before the count is incremented, so other
103    // threads can't see the value exists before being able to read it.
104    MemoryBarrier();
105    AtomicIncrement(&pushed_count_);
106    return true;
107  }
108
109  // Retrieves the oldest value pushed onto the queue. Returns true if there was
110  // an item to peek (the queue was non-empty). This method can be safely called
111  // at the same time as PushBack.
112  bool PeekFront(T* value_out) {
113    if (capacity_ == 0) {
114      LOG(LS_WARNING) << "Queue capacity is 0.";
115      return false;
116    }
117    if (IsEmpty()) {
118      return false;
119    }
120
121    *value_out = data_[popped_count_ % capacity_];
122    return true;
123  }
124
125  // Retrieves the oldest value pushed onto the queue and removes it from the
126  // queue. Returns true if there was an item to pop (the queue was non-empty).
127  // This method can be safely called at the same time as PushBack.
128  bool PopFront(T* value_out) {
129    if (PeekFront(value_out)) {
130      AtomicIncrement(&popped_count_);
131      return true;
132    }
133    return false;
134  }
135
136  // Clears the current items in the queue and sets the new (fixed) size. This
137  // method cannot be called at the same time as any other method.
138  void ClearAndResizeUnsafe(int new_capacity) {
139    capacity_ = new_capacity;
140    data_.reset(new T[new_capacity]);
141    pushed_count_ = 0;
142    popped_count_ = 0;
143  }
144
145  // Returns true if there is no space left in the queue for new elements.
146  int IsFull() const { return pushed_count_ == popped_count_ + capacity_; }
147  // Returns true if there are no elements in the queue.
148  int IsEmpty() const { return pushed_count_ == popped_count_; }
149  // Returns the current number of elements in the queue. This is always in the
150  // range [0, capacity]
151  size_t Size() const { return pushed_count_ - popped_count_; }
152
153  // Returns the capacity of the queue (max size).
154  size_t capacity() const { return capacity_; }
155
156 private:
157  volatile Atomic32 pushed_count_;
158  volatile Atomic32 popped_count_;
159  size_t capacity_;
160  talk_base::scoped_ptr<T[]> data_;
161  DISALLOW_COPY_AND_ASSIGN(FixedSizeLockFreeQueue);
162};
163
164}
165
166#endif  // TALK_BASE_ATOMICOPS_H_
167