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TTaskGroup.cxx
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1// @(#)root/thread:$Id$
2// Author: Danilo Piparo August 2017
3
4/*************************************************************************
5 * Copyright (C) 1995-2017, Rene Brun and Fons Rademakers. *
6 * All rights reserved. *
7 * *
8 * For the licensing terms see $ROOTSYS/LICENSE. *
9 * For the list of contributors see $ROOTSYS/README/CREDITS. *
10 *************************************************************************/
11
12#include "RConfigure.h"
13
14#include "ROOT/TTaskGroup.hxx"
15
16#ifdef R__USE_IMT
17#include "TROOT.h"
18#include "tbb/task_group.h"
19#include "tbb/task_arena.h"
20#endif
21
22#include <type_traits>
23
24/**
25\class ROOT::Experimental::TTaskGroup
26\ingroup Parallelism
27\brief A class to manage the asynchronous execution of work items.
28
29A TTaskGroup represents concurrent execution of a group of tasks.
30Tasks may be dynamically added to the group as it is executing.
31Nesting TTaskGroup instances may result in a runtime overhead.
32*/
33
34namespace ROOT {
35
36namespace Internal {
37
38#ifdef R__USE_IMT
39tbb::task_group *CastToTG(void* p) {
40 return (tbb::task_group *) p;
41}
42
43#endif
44
45} // namespace Internal
46
47namespace Experimental {
48
49using namespace ROOT::Internal;
50
51// in the constructor and destructor the casts are present in order to be able
52// to be independent from the runtime used.
53// This leaves the door open for other TTaskGroup implementations.
54
56{
57#ifdef R__USE_IMT
59 throw std::runtime_error("Implicit parallelism not enabled. Cannot instantiate a TTaskGroup.");
60 }
61 fTaskContainer = ((void *)new tbb::task_group());
62#endif
63}
64
66{
67 *this = std::move(other);
68}
69
71{
72 fTaskContainer = other.fTaskContainer;
73 other.fTaskContainer = nullptr;
74 fCanRun.store(other.fCanRun);
75 return *this;
76}
77
79{
80#ifdef R__USE_IMT
81 if (!fTaskContainer)
82 return;
83 Wait();
85#endif
86}
87
88/////////////////////////////////////////////////////////////////////////////
89/// Cancel all submitted tasks immediately.
91{
92#ifdef R__USE_IMT
93 fCanRun = false;
94 CastToTG(fTaskContainer)->cancel();
95 fCanRun = true;
96#endif
97}
98
99/////////////////////////////////////////////////////////////////////////////
100/// Add to the group an item of work which will be ran asynchronously.
101/// Adding many small items of work to the TTaskGroup is not efficient,
102/// unless they run for long enough. If the work to be done is little, look
103/// try to express nested parallelism or resort to other constructs such as
104/// the TThreadExecutor.
105/// Trying to add a work item to the group while it is in waiting state
106/// makes the method block.
107void TTaskGroup::Run(const std::function<void(void)> &closure)
108{
109#ifdef R__USE_IMT
110 while (!fCanRun)
111 /* empty */;
112
113 CastToTG(fTaskContainer)->run(closure);
114#else
115 closure();
116#endif
117}
118
119/////////////////////////////////////////////////////////////////////////////
120/// Wait until all submitted items of work are completed. This method
121/// is blocking.
123{
124#ifdef R__USE_IMT
125 fCanRun = false;
126 CastToTG(fTaskContainer)->wait();
127 fCanRun = true;
128#endif
129}
130} // namespace Experimental
131} // namespace ROOT
A class to manage the asynchronous execution of work items.
Definition: TTaskGroup.hxx:21
void Run(const std::function< void(void)> &closure)
Add to the group an item of work which will be ran asynchronously.
Definition: TTaskGroup.cxx:107
void Wait()
Wait until all submitted items of work are completed.
Definition: TTaskGroup.cxx:122
void Cancel()
Cancel all submitted tasks immediately.
Definition: TTaskGroup.cxx:90
TTaskGroup & operator=(TTaskGroup &&other)
Definition: TTaskGroup.cxx:70
std::atomic< bool > fCanRun
Definition: TTaskGroup.hxx:32
tbb::task_group * CastToTG(void *p)
Definition: TTaskGroup.cxx:39
void function(const Char_t *name_, T fun, const Char_t *docstring=0)
Definition: RExports.h:151
tbb::task_arena is an alias of tbb::interface7::task_arena, which doesn't allow to forward declare tb...
Definition: StringConv.hxx:21
Bool_t IsImplicitMTEnabled()
Returns true if the implicit multi-threading in ROOT is enabled.
Definition: TROOT.cxx:557