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.
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