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/*=========================================================================
*
* Copyright Insight Software Consortium
*
* 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.txt
*
* 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.
*
*=========================================================================*/
#ifndef itkThreadPool_h
#define itkThreadPool_h
#include "itkConfigure.h"
#include "itkIntTypes.h"
#include <map>
#include <set>
#include <deque>
#include "itkThreadJob.h"
#include "itkObject.h"
#include "itkObjectFactory.h"
#include "itkSimpleFastMutexLock.h"
#include "itkMutexLockHolder.h"
namespace itk
{
/**
* \class ThreadPool
* \brief Thread pool maintains a constant number of threads.
*
* Thread pool is called and initialized from within the MultiThreader.
* Initially the thread pool is started with GlobalDefaultNumberOfThreads.
* The ThreadJob class is used to submit jobs to the thread pool. The ThreadJob's
* necessary members need to be set and then the ThreadJob can be passed to the
* ThreadPool by calling its AddWork method.
* One can then wait for the job by calling the WaitForJob method.
*
* When thread pool is in use by the MultiThreader, invoking SetNumberOfThreads
* on MultiThreader will only increase the number of jobs submitted to the
* ThreadPool, it will not increase the number of threads. This trick can be
* used to increase the number of chunks, which can help load balancing in
* case the algorithm takes more time for some parts of the image, and there
* is relatively small overhead for chunking (splitting the image for processing).
*
* If more threads are required, e.g. in case when Barrier is used,
* AddThreads method should be invoked.
*
* \ingroup OSSystemObjects
* \ingroup ITKCommon
*/
class ITKCommon_EXPORT ThreadPool : public Object
{
public:
/** Standard class typedefs. */
typedef ThreadPool Self;
typedef Object Superclass;
typedef SmartPointer< Self > Pointer;
typedef SmartPointer<const Self> ConstPointer;
typedef ThreadJob::Semaphore Semaphore;
/** Run-time type information (and related methods). */
itkTypeMacro(ThreadPool, Object);
/** Returns the global instance */
static Pointer New();
/** Returns the global singleton instance of the ThreadPool */
static Pointer GetInstance();
/** Add this job to the thread pool queue.
* All data members of the ThreadJob must be filled.
* The semaphore pointer must point to a valid semaphore structure.
* AddWork will initialize that semaphore, and the invoker must pass it
* to WaitForJob in order to wait for the job's completion.
*/
void AddWork(const ThreadJob& job);
/** Can call this method if we want to add extra threads to the pool. */
void AddThreads(ThreadIdType count);
/** The approximate number of idle threads. */
int GetNumberOfCurrentlyIdleThreads() const;
/** This method blocks until the given job has finished executing. */
void WaitForJob(Semaphore& jobSemaphore);
/** Platform specific number of threads */
static ThreadIdType GetGlobalDefaultNumberOfThreadsByPlatform();
/** Examines environment variables and falls back to hyper-threaded core count */
static ThreadIdType GetGlobalDefaultNumberOfThreads();
protected:
static void PlatformCreate(Semaphore &semaphore);
static void PlatformWait(Semaphore &semaphore);
static void PlatformSignal(Semaphore &semaphore);
static void PlatformDelete(Semaphore &semaphore);
static bool PlatformClose(ThreadProcessIdType &threadId); //returns success status
/** Called to add a thread to the thread pool.
This method add a thread to the thread pool and pushes the thread handle
into the m_Threads vector.
*/
void AddThread();
/** Platform-specific function to clean up all the threads. */
void DeleteThreads();
ThreadPool();
virtual ~ThreadPool() ITK_OVERRIDE;
private:
ITK_DISALLOW_COPY_AND_ASSIGN(ThreadPool);
/** Set if exception occurs */
bool m_ExceptionOccurred;
/** This is a list of jobs(ThreadJob) submitted to the thread pool.
* This is the only place where the jobs are submitted.
* Filled by AddWork, emptied by ThreadExecute.
*/
std::deque<ThreadJob> m_WorkQueue;
/** When a thread is idle, it is waiting on m_ThreadsSemaphore.
* AddWork signals this semaphore to resume a (random) thread.
*/
Semaphore m_ThreadsSemaphore;
/** Vector to hold all thread handles.
* Thread handles are used to delete the threads.
*/
std::vector<ThreadProcessIdType> m_Threads;
/** To lock on the internal variables */
static SimpleFastMutexLock m_Mutex;
static Pointer m_ThreadPoolInstance;
/** The continuously running thread function */
static ITK_THREAD_RETURN_TYPE ThreadExecute(void *param);
};
}
#endif
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