lock::try_acquire

Article
06/05/2017

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The latest version of this topic can be found at lock::try_acquire.

Acquires a lock on an object, waiting for a specified amount of time and returning a bool to report the success of acquisition instead of throwing an exception.

Syntax

bool try_acquire(  
   int _timeout_ms  
);  
bool try_acquire(  
   System::TimeSpan _timeout  
);

Parameters

_timeout
Timeout value in milliseconds or as a TimeSpan.

Return Value

true if lock was acquired, false otherwise.

Remarks

If a lock has already been acquired, this function does nothing.

Example

This example uses a single instance of a class across multiple threads. The class uses a lock on itself to ensure that accesses to its internal data are consistent for each thread. The main application thread uses a lock on the same instance of the class to periodically check to see if any worker threads still exist, and waits to exit until all worker threads have completed their tasks.

// msl_lock_try_acquire.cpp  
// compile with: /clr  
#include <msclr/lock.h>  
  
using namespace System;  
using namespace System::Threading;  
using namespace msclr;  
  
ref class CounterClass {  
private:  
   int Counter;     
  
public:  
   property int ThreadCount;  
  
   // function called by multiple threads, use lock to keep Counter consistent  
   // for each thread  
   void UseCounter() {  
      try {  
         lock l(this); // wait infinitely  
  
         Console::WriteLine("In thread {0}, Counter = {1}", Thread::CurrentThread->ManagedThreadId,   
            Counter);  
  
         for (int i = 0; i < 10; i++) {  
            Counter++;  
            Thread::Sleep(10);  
         }  
  
         Console::WriteLine("In thread {0}, Counter = {1}", Thread::CurrentThread->ManagedThreadId,   
            Counter);  
  
         Counter = 0;  
         // lock is automatically released when it goes out of scope and its destructor is called  
      }  
      catch (...) {  
         Console::WriteLine("Couldn't acquire lock!");  
      }  
  
      ThreadCount--;  
   }  
};  
  
int main() {  
   // create a few threads to contend for access to the shared data  
   CounterClass^ cc = gcnew CounterClass;  
   array<Thread^>^ tarr = gcnew array<Thread^>(5);  
   ThreadStart^ startDelegate = gcnew ThreadStart(cc, &CounterClass::UseCounter);  
   for (int i = 0; i < tarr->Length; i++) {  
      tarr[i] = gcnew Thread(startDelegate);  
      cc->ThreadCount++;  
      tarr[i]->Start();  
   }  
  
   // keep our main thread alive until all worker threads have completed  
   lock l(cc, lock_later); // don't lock now, just create the object  
   while (true) {  
      if (l.try_acquire(50)) { // try to acquire lock, don't throw an exception if can't  
         if (0 == cc->ThreadCount) {  
            Console::WriteLine("All threads completed.");  
            break; // all threads are gone, exit while  
         }  
         else {  
            Console::WriteLine("{0} threads exist, continue waiting...", cc->ThreadCount);  
            l.release(); // some threads exist, let them do their work  
         }  
      }  
   }  
}

In thread 3, Counter = 0  
In thread 3, Counter = 10  
In thread 5, Counter = 0  
In thread 5, Counter = 10  
In thread 7, Counter = 0  
In thread 7, Counter = 10  
In thread 4, Counter = 0  
In thread 4, Counter = 10  
In thread 6, Counter = 0  
In thread 6, Counter = 10  
All threads completed.

Requirements

Header file <msclr\lock.h>

Namespace msclr

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