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#ifndef SERIALIZER_H
#define SERIALIZER_H
/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
#include "qpid/Exception.h"
#include "qpid/sys/Runnable.h"
#include "qpid/sys/Monitor.h"
#include "qpid/sys/Thread.h"
#include <boost/function.hpp>
#include <boost/noncopyable.hpp>
#include <deque>
namespace qpid {
namespace sys {
/** Abstract base class for Serializer below. */
class SerializerBase : private boost::noncopyable, private Runnable
{
public:
typedef boost::function<void()> VoidFn0;
struct ShutdownException : public Exception {};
/** @see Serializer::Serializer */
SerializerBase(bool immediate=true);
virtual ~SerializerBase() { shutdown(); }
virtual void dispatch() = 0;
protected:
enum State {
IDLE, ///< No threads are active.
EXECUTING, ///< execute() is executing a single task.
DISPATCHING, ///< dispatch() is draining the queue.
SHUTDOWN ///< SerailizerBase is being destroyed.
};
void shutdown();
void notifyWorker();
void run();
virtual bool empty() = 0;
bool running();
void wait();
Monitor lock;
State state;
bool immediate;
Thread worker;
};
/**
* Execute tasks sequentially, queuing tasks when necessary to
* ensure only one thread at a time executes a task and tasks
* are executed in order.
*
* Task is a void returning 0-arg functor. It must not throw exceptions.
*
* Note we deliberately do not use boost::function as the task type
* because copying a boost::functor allocates the target object on the
* heap.
*/
template <class Task>
class Serializer : public SerializerBase {
std::deque<Task> queue;
bool empty() { return queue.empty(); }
void dispatch(Task& task);
public:
/** Start a serializer.
*
* @param immediate Allow execute() to execute a task immediatly
* in the current thread.
*/
Serializer(bool immediate=true)
: SerializerBase(immediate) {}
~Serializer() { shutdown(); }
/**
* Task may be executed immediately in the calling thread if there
* are no other tasks pending or executing and the "immediate"
* paramater to the constructor was true. Otherwise task will be
* enqueued for execution by a dispatch thread.
*/
void execute(Task& task);
/** Execute pending tasks sequentially in calling thread.
* Drains the task queue and returns, does not block for more tasks.
*
* @exception ShutdownException if the serializer is being destroyed.
*/
void dispatch();
};
template <class Task>
void Serializer<Task>::execute(Task& task) {
Mutex::ScopedLock l(lock);
assert(state != SHUTDOWN);
if (immediate && state == IDLE) {
state = EXECUTING;
dispatch(task);
if (state != SHUTDOWN) {
assert(state == EXECUTING);
state = IDLE;
}
}
else
queue.push_back(task);
if (!queue.empty() && state == IDLE) {
state = DISPATCHING;
notifyWorker();
}
}
template <class Task>
void Serializer<Task>::dispatch() {
Mutex::ScopedLock l(lock);
// TODO aconway 2007-07-16: This loop could be unbounded
// if other threads add work while we're in dispatch(Task&).
// If we need to bound it we could dispatch just the elements
// that were enqueued when dispatch() was first called - save
// begin() iterator and pop only up to that.
while (!queue.empty() && state != SHUTDOWN) {
assert(state == DISPATCHING);
dispatch(queue.front());
queue.pop_front();
}
if (state != SHUTDOWN) {
assert(state == DISPATCHING);
state = IDLE;
}
}
template <class Task>
void Serializer<Task>::dispatch(Task& task) {
// Preconditions: lock is held, state is EXECUTING or DISPATCHING
assert(state != IDLE);
assert(state != SHUTDOWN);
assert(state == EXECUTING || state == DISPATCHING);
Mutex::ScopedUnlock u(lock);
// No exceptions allowed in task.
notifyWorker();
try { task(); } catch (...) { assert(0); }
}
}} // namespace qpid::sys
#endif /*!SERIALIZER_H*/
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