ThreadWeaver

resourcerestrictionpolicy.h
1 /* -*- C++ -*-
2  This file declares the ResourceRestrictionPolicy class.
3 
4  SPDX-FileCopyrightText: 2004-2013 Mirko Boehm <[email protected]>
5 
6  SPDX-License-Identifier: LGPL-2.0-or-later
7 
8  $Id: Job.h 32 2005-08-17 08:38:01Z mirko $
9 */
10 
11 #ifndef RESOURCE_RESTRICTION_POLICY_H
12 #define RESOURCE_RESTRICTION_POLICY_H
13 
14 #include <QtGlobal>
15 
16 #include "jobpointer.h"
17 #include "queuepolicy.h"
18 
19 namespace ThreadWeaver
20 {
21 class JobInterface;
22 
23 /** @brief ResourceRestrictionPolicy is used to limit the number of concurrent accesses to the same resource.
24  *
25  * If a set of Jobs accesses a resource that can be overloaded, this may degrade application performance. For
26  * example, loading too many files from the hard disc at the same time may lead to longer load times.
27  * ResourceRestrictionPolicy can be used to cap the number of accesses. Resource restriction policies are
28  * shared between the affected jobs. All jobs that share a resource restriction policy have to acquire
29  * permission from the policy before they can run. In this way, resource restrictions can be compared to
30  * semaphores, only that they require no locking at the thread level.
31  * The example uses a resource restriction to limit the number of images files that are loaded from
32  * the disk at the same time.
33  */
34 
35 class THREADWEAVER_EXPORT ResourceRestrictionPolicy : public QueuePolicy
36 {
37 public:
38  explicit ResourceRestrictionPolicy(int cap = 0);
39  ~ResourceRestrictionPolicy() override;
40 
41  /** @brief Cap the number of simultaneously executing jobs.
42  * Capping the amount of jobs will make sure that at max the number of jobs executing at any time is
43  * limited to the capped amount. Note that immediately after setting the amount of running jobs may be
44  * higher than the set amount. This setting only limits the starting of new jobs.
45  * @param newCap the new cap to limit the amount of parallel jobs.
46  */
47  void setCap(int newCap);
48  int cap() const;
49  bool canRun(JobPointer) override;
50  void free(JobPointer) override;
51  void release(JobPointer) override;
52  void destructed(JobInterface *job) override;
53 
54 private:
55  class Private;
56  Private *const d;
57 };
58 
59 }
60 
61 #endif // RESOURCE_RESTRICTION_POLICY_H
virtual void release(quint64 objid)
QueuePolicy is an interface for customizations of the queueing behaviour of jobs.
Definition: queuepolicy.h:38
ResourceRestrictionPolicy is used to limit the number of concurrent accesses to the same resource.
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