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/*
* libjingle
* Copyright 2011, Google Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef TALK_BASE_ATOMICOPS_H_
#define TALK_BASE_ATOMICOPS_H_
#include <string>
#include "talk/base/basictypes.h"
#include "talk/base/common.h"
#include "talk/base/logging.h"
#include "talk/base/scoped_ptr.h"
namespace talk_base {
// 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_;
talk_base::scoped_ptr<T[]> data_;
DISALLOW_COPY_AND_ASSIGN(FixedSizeLockFreeQueue);
};
}
#endif // TALK_BASE_ATOMICOPS_H_
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