std:: try_lock
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Defined in header
<mutex>
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||
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, no further call to
try_lock
is performed,
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 <chrono> #include <functional> #include <iostream> #include <mutex> #include <thread> #include <vector> 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) |