| Defined in header <mutex> | ||
|---|---|---|
template< class Lockable1, class Lockable2, class... LockableN> int try_lock( Lockable1& lock1, Lockable2& lock2, LockableN&... lockn); | (since C++11) |
Tries to lock each of the given Lockable objects lock1, lock2, ..., lockn by calling try_lock in order beginning with the first.
If a call to try_lock fails, unlock is called for any locked objects and a 0-based index of the object that failed to lock is returned.
If a call to try_lock results in an exception, unlock is called for any locked objects before rethrowing.
Parameters
| lock1, lock2, ... , lockn | - | the Lockable objects to lock |
Return value
-1 on success, or 0-based index value of the object that failed to lock.
Example
The following example uses std::try_lock to periodically tally and reset counters running in separate threads.
#include <mutex>
#include <vector>
#include <thread>
#include <iostream>
#include <functional>
#include <chrono>
int main()
{
int foo_count = 0;
std::mutex foo_count_mutex;
int bar_count = 0;
std::mutex bar_count_mutex;
int overall_count = 0;
bool done = false;
std::mutex done_mutex;
auto increment = [](int &counter, std::mutex &m, const char *desc) {
for (int i = 0; i < 10; ++i) {
std::unique_lock<std::mutex> lock(m);
++counter;
std::cout << desc << ": " << counter << '\n';
lock.unlock();
std::this_thread::sleep_for(std::chrono::seconds(1));
}
};
std::thread increment_foo(increment, std::ref(foo_count),
std::ref(foo_count_mutex), "foo");
std::thread increment_bar(increment, std::ref(bar_count),
std::ref(bar_count_mutex), "bar");
std::thread update_overall([&]() {
done_mutex.lock();
while (!done) {
done_mutex.unlock();
int result = std::try_lock(foo_count_mutex, bar_count_mutex);
if (result == -1) {
overall_count += foo_count + bar_count;
foo_count = 0;
bar_count = 0;
std::cout << "overall: " << overall_count << '\n';
foo_count_mutex.unlock();
bar_count_mutex.unlock();
}
std::this_thread::sleep_for(std::chrono::seconds(2));
done_mutex.lock();
}
done_mutex.unlock();
});
increment_foo.join();
increment_bar.join();
done_mutex.lock();
done = true;
done_mutex.unlock();
update_overall.join();
std::cout << "Done processing\n"
<< "foo: " << foo_count << '\n'
<< "bar: " << bar_count << '\n'
<< "overall: " << overall_count << '\n';
}Possible output:
bar: 1 foo: 1 foo: 2 bar: 2 foo: 3 overall: 5 bar: 1 foo: 1 bar: 2 foo: 2 bar: 3 overall: 10 bar: 1 foo: 1 bar: 2 foo: 2 overall: 14 bar: 1 foo: 1 bar: 2 overall: 17 foo: 1 bar: 1 foo: 2 overall: 20 Done processing foo: 0 bar: 0 overall: 20
See also
| (C++11) | locks specified mutexes, blocks if any are unavailable (function template) |
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