std::mutex::try_lock

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Concurrency support library

Threads thread (C++11) jthread (C++20) hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17) this_thread namespace get_id (C++11) yield (C++11) sleep_for (C++11) sleep_until (C++11) Cooperative cancellation stop_token (C++20) inplace_stop_token (C++26) never_stop_token (C++26) stop_source (C++20) inplace_stop_source (C++26)   stop_callback (C++20) inplace_stop_callback (C++26) stop_callback_for_t (C++26) stoppable_token (C++26) unstoppable_token (C++26) stoppable-source (C++26) stoppable-callback-for (C++26)   Mutual exclusion mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17) timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14) Generic lock management lock (C++11) lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) once_flag (C++11) call_once (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lockdefer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)(C++11)(C++11)(C++11) Condition variables condition_variable (C++11) condition_variable_any (C++11) notify_all_at_thread_exit (C++11) cv_status (C++11) Semaphores counting_semaphorebinary_semaphore (C++20)(C++20) Latches and Barriers latch (C++20) barrier (C++20) Futures promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11) launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11) Safe Reclamation rcu_obj_base (C++26) rcu_domain (C++26) rcu_default_domain (C++26) rcu_synchronize (C++26) rcu_barrier (C++26) rcu_retire (C++26) Hazard Pointers hazard_pointer_obj_base (C++26) hazard_pointer (C++26) make_hazard_pointer (C++26)

Atomic types atomic (C++11) atomic_ref (C++20) atomic_flag (C++11) Initialization of atomic types atomic_init (C++11)(deprecated in C++20) ATOMIC_VAR_INIT (C++11)(deprecated in C++20) ATOMIC_FLAG_INIT (C++11) Memory ordering memory_order (C++11) kill_dependency (C++11) atomic_thread_fence (C++11) atomic_signal_fence (C++11) Free functions for atomic operations atomic_storeatomic_store_explicit (C++11)(C++11) atomic_loadatomic_load_explicit (C++11)(C++11) atomic_exchangeatomic_exchange_explicit (C++11)(C++11) atomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_compare_exchange_strong_explicit (C++11)(C++11)(C++11)(C++11) atomic_fetch_addatomic_fetch_add_explicit (C++11)(C++11) atomic_fetch_subatomic_fetch_sub_explicit (C++11)(C++11) atomic_fetch_andatomic_fetch_and_explicit (C++11)(C++11) atomic_fetch_oratomic_fetch_or_explicit (C++11)(C++11) atomic_fetch_xoratomic_fetch_xor_explicit (C++11)(C++11) atomic_fetch_maxatomic_fetch_max_explicit (C++26)(C++26) atomic_fetch_minatomic_fetch_min_explicit (C++26)(C++26) atomic_is_lock_free (C++11) atomic_waitatomic_wait_explicit (C++20)(C++20) atomic_notify_one (C++20) atomic_notify_all (C++20) Free functions for atomic flags atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C++11)(C++11) atomic_flag_clearatomic_flag_clear_explicit (C++11)(C++11) atomic_flag_testatomic_flag_test_explicit (C++20)(C++20) atomic_flag_waitatomic_flag_wait_explicit (C++20)(C++20) atomic_flag_notify_one (C++20) atomic_flag_notify_all (C++20)

 

std::mutex

Member functions

mutex::mutex

mutex::~mutex

Locking

mutex::lock

mutex::try_lock

mutex::unlock

Native handle

mutex::native_handle

 

bool try_lock();		(since C++11)

Tries to lock the mutex. Returns immediately. On successful lock acquisition returns true, otherwise returns false.

This function is allowed to fail spuriously and return false even if the mutex is not currently locked by any other thread.

If try_lock is called by a thread that already owns the mutex, the behavior is undefined.

Prior unlock() operation on the same mutex synchronizes-with (as defined in std::memory_order) this operation if it returns true. Note that prior lock() does not synchronize with this operation if it returns false.

Parameters

(none)

Return value

true if the lock was acquired successfully, otherwise false.

Exceptions

Throws nothing.

Example

Run this code

#include <chrono>
#include <iostream> // std::cout
#include <mutex>
#include <thread>
 
std::chrono::milliseconds interval(100);
 
std::mutex mutex;
int job_shared = 0; // both threads can modify 'job_shared',
                    // mutex will protect this variable
 
int job_exclusive = 0; // only one thread can modify 'job_exclusive'
                       // no protection needed
 
// this thread can modify both 'job_shared' and 'job_exclusive'
void job_1() 
{
    std::this_thread::sleep_for(interval); // let 'job_2' take a lock
 
    while (true)
    {
        // try to lock mutex to modify 'job_shared'
        if (mutex.try_lock())
        {
            std::cout << "job shared (" << job_shared << ")\n";
            mutex.unlock();
            return;
        }
        else
        {
            // can't get lock to modify 'job_shared'
            // but there is some other work to do
            ++job_exclusive;
            std::cout << "job exclusive (" << job_exclusive << ")\n";
            std::this_thread::sleep_for(interval);
        }
    }
}
 
// this thread can modify only 'job_shared'
void job_2() 
{
    mutex.lock();
    std::this_thread::sleep_for(5 * interval);
    ++job_shared;
    mutex.unlock();
}
 
int main() 
{
    std::thread thread_1(job_1);
    std::thread thread_2(job_2);
 
    thread_1.join();
    thread_2.join();
}

Possible output:

job exclusive (1)
job exclusive (2)
job exclusive (3)
job exclusive (4)
job shared (1)

See also

lock	locks the mutex, blocks if the mutex is not available (public member function)
unlock	unlocks the mutex (public member function)
C documentation for mtx_trylock