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TSemaphore.cxx
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1 // @(#)root/thread:$Id$
2 // Author: Fons Rademakers 02/07/97 (Revised: G Ganis, Nov 2015)
3 
4 /*************************************************************************
5  * Copyright (C) 1995-2000, 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 //////////////////////////////////////////////////////////////////////////
13 // //
14 // TSemaphore //
15 // //
16 // This class implements a counting semaphore. Use a semaphore //
17 // to synchronize threads. //
18 // //
19 //////////////////////////////////////////////////////////////////////////
20 
21 #include "TSemaphore.h"
22 
23 ////////////////////////////////////////////////////////////////////////////////
24 /// Create counting semaphore.
25 
26 TSemaphore::TSemaphore(Int_t initial) : fValue(initial), fWakeups(0)
27 {
28 }
29 
30 ////////////////////////////////////////////////////////////////////////////////
31 /// If the semaphore value is > 0 then decrement it and carry on, else block,
32 /// waiting on the condition until it is signaled.
33 /// Returns always 0, for backward compatibility with the first implementation.
34 
36 {
37  std::unique_lock<std::mutex> lk(fMutex);
38  fValue--;
39 
40  if (fValue < 0) {
41  do {
42  fCond.wait(lk);
43  } while (fWakeups < 1);
44  // We have been waken-up: decrease the related counter
45  fWakeups--;
46  }
47  return 0;
48 }
49 
50 ////////////////////////////////////////////////////////////////////////////////
51 /// If the semaphore value is > 0 then decrement it and carry on, else block.
52 /// If millisec > 0 then a relative timeout of millisec milliseconds is applied.
53 /// For backward compatibility with the first implementation, millisec == 0 means
54 /// no timeout.
55 /// Returns 1 if timed-out, 0 otherwise.
56 
58 {
59  // For backward compatibility with the first implementation
60  if (millisec <= 0) return Wait();
61 
62  Int_t rc= 0;
63  std::unique_lock<std::mutex> lk(fMutex);
64  fValue--;
65 
66  if (fValue < 0) {
67  std::cv_status cvs = std::cv_status::timeout;
68  do {
69  cvs = fCond.wait_for(lk,std::chrono::milliseconds(millisec));
70  } while (fWakeups < 1 && cvs != std::cv_status::timeout);
71  if (cvs == std::cv_status::timeout) {
72  // Give back the token ...
73  fValue++;
74  rc = 1;
75  } else {
76  // We have been waken-up: decrease the related counter
77  fWakeups--;
78  }
79  }
80  return rc;
81 }
82 
83 ////////////////////////////////////////////////////////////////////////////////
84 /// If the semaphore value is > 0 then decrement it and return 0. If it's
85 /// already 0 then return 1. This call never blocks.
86 
88 {
89  std::unique_lock<std::mutex> lk(fMutex);
90  if (fValue > 0) {
91  fValue--;
92  } else {
93  return 1;
94  }
95  return 0;
96 }
97 
98 ////////////////////////////////////////////////////////////////////////////////
99 /// Increment the value of the semaphore. If any threads are blocked in Wait(),
100 /// wakeup one of them.
101 /// Returns always 0, for backward compatibility with the first implementation.
102 
104 {
105  std::unique_lock<std::mutex> lk(fMutex);
106  fValue++;
107 
108  if (fValue <= 0) {
109  // There were threads waiting: wake up one
110  fWakeups++;
111  fCond.notify_one();
112  }
113  return 0;
114 }
std::mutex fMutex
Definition: TSemaphore.h:32
Int_t TryWait()
If the semaphore value is > 0 then decrement it and return 0.
Definition: TSemaphore.cxx:87
int Int_t
Definition: RtypesCore.h:41
std::condition_variable fCond
Definition: TSemaphore.h:33
UInt_t fWakeups
Definition: TSemaphore.h:35
Int_t Wait()
If the semaphore value is > 0 then decrement it and carry on, else block, waiting on the condition un...
Definition: TSemaphore.cxx:35
TSemaphore(const TSemaphore &s)=delete
PyObject * fValue
Int_t Post()
Increment the value of the semaphore.
Definition: TSemaphore.cxx:103
Int_t fValue
Definition: TSemaphore.h:34