std::once_flag

 

C++

編譯器支援

自由（freestanding）與宿主（hosted）

語言

標準庫

標準庫標頭檔案

具名要求

特性測試宏 (C++20)

語言支援庫

概念庫 (C++20)

診斷庫

記憶體管理庫

超程式設計庫 (C++11)

通用工具庫

容器庫

迭代器庫

範圍庫 (C++20)

演算法庫

字串庫

文字處理庫

數值庫

日期和時間庫

輸入/輸出庫

檔案系統庫 (C++17)

併發支援庫 (C++11)

執行控制庫 (C++26)

技術規範

符號索引

外部庫

 

併發支援庫

執行緒 thread (C++11) jthread (C++20) hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17) this_thread 名稱空間 get_id (C++11) yield (C++11) sleep_for (C++11) sleep_until (C++11) 協同取消 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)   互斥 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) 通用鎖管理 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) 條件變數 condition_variable (C++11) condition_variable_any (C++11) notify_all_at_thread_exit (C++11) cv_status (C++11) 訊號量 counting_semaphorebinary_semaphore (C++20)(C++20) 門閂和屏障 latch (C++20) barrier (C++20) 期值 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) 安全回收 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) 危險指標 hazard_pointer_obj_base (C++26) hazard_pointer (C++26) make_hazard_pointer (C++26)

原子型別 atomic (C++11) atomic_ref (C++20) atomic_flag (C++11) 原子型別的初始化 atomic_init (C++11)(C++20 中已棄用) ATOMIC_VAR_INIT (C++11)(C++20 中已棄用) ATOMIC_FLAG_INIT (C++11) 記憶體排序 memory_order (C++11) kill_dependency (C++11)(C++26 中已棄用) atomic_thread_fence (C++11) atomic_signal_fence (C++11) 原子操作的自由函式 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) 原子標誌的自由函式 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)

 

定義於標頭檔案 <mutex>
class once_flag;		(C++11 起)

類 std::once_flag 是 std::call_once 的一個輔助結構。

一個 std::once_flag 型別的物件，如果被傳遞給多個 std::call_once 呼叫，將允許這些呼叫相互協調，從而只有一個呼叫能夠實際完成。

std::once_flag 既不可複製也不可移動。

成員函式

std::once_flag::once_flag

constexpr once_flag() noexcept;

構造一個 once_flag 物件。內部狀態被設定為表示尚未呼叫任何函式。

引數

(無)

參見

call_once (C++11)	即使從多個執行緒呼叫，也只調用一次函式 (函式模板)
C 文件 關於 once_flag