std::thread::hardware_concurrency

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Feature test macros(C++20)
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Concepts library(C++20)
Diagnostics library
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Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
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Symbols index
External libraries

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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)

(C++20)

(C++20)

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)(deprecated in C++26)
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)

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std::thread

Member classes
thread::id
Member functions
thread::thread
thread::~thread
thread::operator=
Observers
thread::joinable
thread::get_id
thread::native_handle
thread::hardware_concurrency
Operations
thread::join
thread::detach
thread::swap
Non-member functions
swap(std::thread) (C++11)

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staticunsignedint hardware_concurrency()noexcept;		(since C++11)

Returns the number of concurrent threads supported by the implementation. The value should be considered only a hint.

[edit]Parameters

(none)

[edit]Return value

Number of concurrent threads supported. If the value is not well defined or not computable, returns0.

[edit]Example

Run this code

#include <iostream>#include <thread> int main(){unsignedint n= std::thread::hardware_concurrency();std::cout<< n<<" concurrent threads are supported.\n";}