Thread support library

 

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)

 

C++ includes built-in support for threads, mutual exclusion, condition variables, and futures.

Threads

Threads enable programs to execute across several processor cores.

Defined in header <thread>
thread (C++11)	manages a separate thread (class)
jthread (C++20)	std::thread with support for auto-joining and cancellation (class)
Functions managing the current thread
Defined in namespace this_thread
yield (C++11)	suggests that the implementation reschedule execution of threads (function)
get_id (C++11)	returns the thread id of the current thread (function)
sleep_for (C++11)	stops the execution of the current thread for a specified time duration (function)
sleep_until (C++11)	stops the execution of the current thread until a specified time point (function)

Thread cancellation The stop_XXX types are designed to enable thread cancellation for std::jthread, although they can also be used independently of std::jthread - for example to interrupt std::condition_variable_any waiting functions, or for a custom thread management implementation. In fact they do not even need to be used to "stop" anything, but can instead be used for a thread-safe one-time function(s) invocation trigger, for example. Defined in header <stop_token> stop_token (C++20) an interface for querying if a std::jthread cancellation request has been made (class) stop_source (C++20) class representing a request to stop one or more std::jthreads (class) stop_callback (C++20) an interface for registering callbacks on std::jthread cancellation (class template)

(since C++20)

Cache size access

Defined in header <new>
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)	min offset to avoid false sharing max offset to promote true sharing (constant)

Mutual exclusion

Mutual exclusion algorithms prevent multiple threads from simultaneously accessing shared resources. This prevents data races and provides support for synchronization between threads.

Defined in header <mutex>
mutex (C++11)	provides basic mutual exclusion facility (class)
timed_mutex (C++11)	provides mutual exclusion facility which implements locking with a timeout (class)
recursive_mutex (C++11)	provides mutual exclusion facility which can be locked recursively by the same thread (class)
recursive_timed_mutex (C++11)	provides mutual exclusion facility which can be locked recursively by the same thread and implements locking with a timeout (class)
Defined in header <shared_mutex>
shared_mutex (C++17)	provides shared mutual exclusion facility (class)
shared_timed_mutex (C++14)	provides shared mutual exclusion facility and implements locking with a timeout (class)
Generic mutex management
Defined in header <mutex>
lock_guard (C++11)	implements a strictly scope-based mutex ownership wrapper (class template)
scoped_lock (C++17)	deadlock-avoiding RAII wrapper for multiple mutexes (class template)
unique_lock (C++11)	implements movable mutex ownership wrapper (class template)
shared_lock (C++14)	implements movable shared mutex ownership wrapper (class template)
defer_locktry_to_lockadopt_lockdefer_lock_ttry_to_lock_tadopt_lock_t (C++11)	tags used to specify locking strategy (tag)
Generic locking algorithms
try_lock (C++11)	attempts to obtain ownership of mutexes via repeated calls to try_lock (function template)
lock (C++11)	locks specified mutexes, blocks if any are unavailable (function template)
Call once
once_flag (C++11)	helper object to ensure that call_once invokes the function only once (class)
call_once (C++11)	invokes a function only once even if called from multiple threads (function template)

Condition variables

A condition variable is a synchronization primitive that allows multiple threads to communicate with each other. It allows some number of threads to wait (possibly with a timeout) for notification from another thread that they may proceed. A condition variable is always associated with a mutex.

Defined in header <condition_variable>
condition_variable (C++11)	provides a condition variable associated with a std::unique_lock (class)
condition_variable_any (C++11)	provides a condition variable associated with any lock type (class)
notify_all_at_thread_exit (C++11)	schedules a call to notify_all to be invoked when this thread is completely finished (function)
cv_status (C++11)	lists the possible results of timed waits on condition variables (enum)

Semaphores A semaphore is a lightweight synchronization primitive used to constrain concurrent access to a shared resource. When it's possible to use both, semaphore can be more efficient than condition variable. Defined in header <semaphore> counting_semaphore (C++20) semaphore that models a non-negative resource count (class template) binary_semaphore (C++20) semaphore that has only two states (typedef) Latches and Barriers Latches and barriers are thread coordination mechanism that allows any number of threads to block until an expected number of threads arrive at the barrier. Latches cannot be reused, barriers can be used repeatedly. Defined in header <latch> latch (C++20) single-use thread barrier (class) Defined in header <barrier> barrier (C++20) reusable thread barrier (class template)

(since C++20)

Futures

The standard library provides facilities to obtain values that are returned and to catch exceptions that are thrown by asynchronous tasks (i.e. functions launched in separate threads). These values are communicated in a shared state, in which the asynchronous task may write its return value or store an exception, and which may be examined, waited for, and otherwise manipulated by other threads that hold instances of std::future or std::shared_future that reference that shared state.

Defined in header <future>
promise (C++11)	stores a value for asynchronous retrieval (class template)
packaged_task (C++11)	packages a function to store its return value for asynchronous retrieval (class template)
future (C++11)	waits for a value that is set asynchronously (class template)
shared_future (C++11)	waits for a value (possibly referenced by other futures) that is set asynchronously (class template)
async (C++11)	runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result (function template)
launch (C++11)	specifies the launch policy for std::async (enum)
future_status (C++11)	specifies the results of timed waits performed on std::future and std::shared_future (enum)
Future errors
future_error (C++11)	reports an error related to futures or promises (class)
future_category (C++11)	identifies the future error category (function)
future_errc (C++11)	identifies the future error codes (enum)

See also

C documentation for Thread support library