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// @file background.h
/* Copyright 2009 10gen Inc.
*
* Licensed 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.
*/
#pragma once
namespace mongo {
/**
* Background thread dispatching.
* subclass and define run()
*
* It is ok to call go(), that is, run the job, more than once -- if the
* previous invocation has finished. Thus one pattern of use is to embed
* a backgroundjob in your object and reuse it (or same thing with
* inheritance). Each go() call spawns a new thread.
*
* Thread safety:
* note when job destructs, the thread is not terminated if still running.
* generally if the thread could still be running, allocate the job dynamically
* and set deleteSelf to true.
*
* go() and wait() are not thread safe
* run() will be executed on the background thread
* BackgroundJob object must exist for as long the background thread is running
*/
class BackgroundJob : boost::noncopyable {
protected:
/**
* sub-class must intantiate the BackgrounJob
*
* @param selfDelete if set to true, object will destruct itself after the run() finished
* @note selfDelete instantes cannot be wait()-ed upon
*/
explicit BackgroundJob(bool selfDelete = false);
virtual string name() const = 0;
/**
* define this to do your work.
* after this returns, state is set to done.
* after this returns, deleted if deleteSelf true.
*
* NOTE:
* if run() throws, the exception will be caught within 'this' object and will ultimately lead to the
* BackgroundJob's thread being finished, as if run() returned.
*
*/
virtual void run() = 0;
public:
enum State {
NotStarted,
Running,
Done
};
virtual ~BackgroundJob() { }
/**
* starts job.
* returns immediatelly after dispatching.
*
* @note the BackgroundJob object must live for as long the thread is still running, ie
* until getState() returns Done.
*/
BackgroundJob& go();
/**
* wait for completion.
*
* @param msTimeOut maximum amount of time to wait in millisecons
* @return true if did not time out. false otherwise.
*
* @note you can call wait() more than once if the first call times out.
* but you cannot call wait on a self-deleting job.
*/
bool wait( unsigned msTimeOut = 0 );
// accessors
State getState() const;
bool running() const;
private:
struct JobStatus;
boost::shared_ptr<JobStatus> _status; // shared between 'this' and body() thread
void jobBody( boost::shared_ptr<JobStatus> status );
};
} // namespace mongo
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