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Algorithms Algorithms(算法) bsearch bsearch_s qsort qsort_s Atomic operations Atomic operations library(原子操作庫) ATOMIC_*_LOCK_FREE atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_exchange atomic_exchange_explicit atomic_fetch_add atomic_fetch_add_explicit atomic_fetch_and atomic_fetch_and_explicit atomic_fetch_or atomic_fetch_or_explicit atomic_fetch_sub atomic_fetch_sub_explicit atomic_fetch_xor atomic_fetch_xor_explicit atomic_flag atomic_flag_clear atomic_flag_clear_explicit ATOMIC_FLAG_INIT atomic_flag_test_and_set atomic_flag_test_and_set_explicit atomic_init atomic_is_lock_free atomic_load atomic_load_explicit atomic_signal_fence atomic_store atomic_store_explicit atomic_thread_fence(線程圍欄) ATOMIC_VAR_INIT kill_dependency memory_order(內(nèi)存排序) C keywords auto(自動存儲) break(跳出循環(huán)) C keywords(關(guān)鍵詞) case char const(常量修飾符) continue default(預(yù)設(shè)運算式) do double(雙精度浮點型) else enum(枚舉類型) extern(全局變量) float(浮點數(shù)) for fortran goto(goto語句) if(if語句) inline(行內(nèi)函式) int long(長整型) register(寄存器變量) restrict( restrict類型限定符) return short signed sizeof(sizeof運算符) static(靜態(tài)變量) struct(結(jié)構(gòu)體) switch(switch語句) typedef(typedef關(guān)鍵字) union(聯(lián)合體) unsigned(無符號) void(空類型) volatile(volatile變量) while(while語句) _Alignas _Alignof _Atomic _Bool _Complex _Generic _Imaginary _Noreturn _Static_assert _Thread_local C language #define directive #elif directive #else directive #endif directive #error directive #if directive #ifdef directive #ifndef directive #include directive #line directive #pragma directive alignas(對齊指定符) Alternative operators and tokens(替代運算符和令牌) Analyzability Arithmetic operators Arithmetic types Array declaration(數(shù)組聲明) Array initialization(陣列初始化) ASCII Chart Assignment operators(賦值運算符) types(atomic類型限定符) Basic concepts Bit fields(位域) break statement C language C Operator Precedence cast operator character constant(字符字面量) Comments(注釋符) Comparison operators(比較運算符) compound literals(符合字面量) Conditional inclusion(條件包含) Conformance(一致性) const type qualifier(const 限定符) Constant expressions(常量表達(dá)) continue statement Declarations(聲明) do-while loop Enumerations(枚舉類型) Escape sequences(轉(zhuǎn)義字符) Expressions(表達(dá)式) External and tentative definitions(外部和暫定的定義) File scope(文件范圍) floating constant(浮點常量) for loop Function declarations(函數(shù)聲明) Function definitions(函數(shù)聲明) Functions Generic selection泛型選擇 goto statement Identifier(標(biāo)示符) if statement Implicit conversions(隱式轉(zhuǎn)換) Increment/decrement operators(前置/后置操作符) Initialization(初始化) inline function specifier(內(nèi)聯(lián)函式) integer constant Lifetime(生命期) Logical operators(邏輯運算符) Lookup and name spaces Main function(主函式) Member access operators(會員接入運營商) Memory model Objects and alignment(字節(jié)對齊) Order of evaluation(評估順序) Other operators Phases of translation(翻譯階段) Pointer declaration Preprocessor(預(yù)處理) restrict type qualifier(restrict類型限定符) return statement Scalar initialization(標(biāo)量類型初始化) Scope(范圍) sizeof operator(sizeof運算符) Statements(陳述) static assert declaration(靜態(tài)斷言聲明) Static storage duration(靜態(tài)存儲周期) Storage-class specifiers(存儲類說明符) string literals(字符串字面量) Struct and union initialization(結(jié)構(gòu)體與聯(lián)合體初始化) Struct declaration(結(jié)構(gòu)體聲明) switch statement Thread storage duration(線程存儲時間) Type Type(類型) Typedef declaration(Typedef聲明) Undefined behavior(未定義行為) Union declaration(聯(lián)合體聲明) Value categories(值類別) Variadic arguments(變長參數(shù)宏) volatile type qualifier(volatile 類型限定符) while loop _Alignof operator _Noreturn function specifier Date and time asctime(asctime函數(shù)) asctime_s clock CLOCKS_PER_SEC clock_t ctime(ctime函數(shù)) ctime_s Date and time utilities(日期和時間庫) difftime(計算兩個時間的間隔) gmtime gmtime_s localtime localtime_s mktime(將時間結(jié)構(gòu)數(shù)據(jù)轉(zhuǎn)換成經(jīng)過的秒數(shù)的函數(shù)) strftime(格式化輸出時間函數(shù)) time timespec timespec_get time_t tm wcsftime(格式化時間寬字符) Dynamic memory management aligned_alloc C memory management library(內(nèi)存管理庫) calloc free(釋放動態(tài)分配空間的函數(shù)) malloc(動態(tài)分配內(nèi)存空間的函數(shù)) realloc(重新分配內(nèi)存空間的函數(shù)) Error handling abort_handler_s assert(斷言) constraint_handler_t errno(錯誤報告) Error handling(錯誤處理) Error numbers(錯誤個數(shù)) ignore_handler_s set_constraint_handler_s static_assert File input/output clearerr(清除/復(fù)位) fclose feof ferror fflush(清空文件緩沖區(qū)) fgetc fgetpos fgets fgetwc fgetws File input/output fopen fopen_s fprintf fprintf_s fputc fputs fputwc fputws fread freopen freopen_s fscanf fscanf_s fseek fsetpos ftell fwide fwprintf fwprintf_s fwrite fwscanf fwscanf_s getc getchar gets gets_s getwchar perror printf printf_s putc putchar puts putwc putwchar remove rename rewind scanf scanf_s setbuf setvbuf snprintf sprintf sscanf sscanf_s swprintf swprintf_s swscanf swscanf_s tmpfile tmpfile_s tmpnam tmpnam_s ungetc ungetwc vfprintf vfprintf_s vfscanf vfscanf_s vfwprintf vfwprintf_s vfwscanf vfwscanf_s vprintf vprintf_s vscanf vscanf_s vsnprintf vsprintf vsscanf vsscanf_s vswprintf vswprintf_s vswscanf vswscanf_s vwprintf vwprintf_s vwscanf vwscanf_s wprintf wprintf_s wscanf wscanf_s Localization support lconv LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME localeconv Localization support setlocale Numerics abs acos acosf acosh acoshf acoshl acosl asin asinf asinh asinhf asinhl asinl atan atan2 atan2f atan2l atanf atanh atanhf atanhl atanl cabs cabsf cabsl cacos cacosf cacosh cacoshf cacoshl cacosl carg cargf cargl casin casinf casinh casinhf casinhl casinl catan catanf catanh catanhf catanhl catanl cbrt cbrtf cbrtl ccos ccosf ccosh ccoshf ccoshl ccosl ceil ceilf ceill cexp cexpf cexpl cimag cimagf cimagl clog clogf clogl CMPLX CMPLXF CMPLXL Common mathematical functions complex Complex number arithmetic conj conjf conjl copysign copysignf copysignl cos cosf cosh coshf coshl cosl cpow cpowf cpowl cproj cprojf cprojl creal crealf creall csin csinf csinh csinhf csinhl csinl csqrt csqrtf csqrtl ctan ctanf ctanh ctanhf ctanhl ctanl div double_t erf erfc erfcf erfcl erff erfl exp exp2 exp2f exp2l expf expl expm1 expm1f expm1l fabs fabsf fabsl fdim feclearexcept fegetenv fegetexceptflag fegetround feholdexcept feraiseexcept fesetenv fesetexceptflag fesetround fetestexcept feupdateenv FE_ALL_EXCEPT FE_DFL_ENV FE_DIVBYZERO FE_DOWNWARD FE_INEXACT FE_INVALID FE_OVERFLOW FE_TONEAREST FE_TOWARDZERO FE_UNDERFLOW FE_UPWARD Floating-point environment float_t floor floorf floorl fma fmaf fmal fmax fmaxf fmaxl fmin fminf fminl fmod fmodf fmodl fpclassify FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO frexp frexpf frexpl HUGE_VAL HUGE_VALF HUGE_VALL hypot hypotf hypotl I ilogb ilogbf ilogbl imaginary imaxabs imaxdiv INFINITY isfinite isgreater isgreaterequal isinf isless islessequal islessgreater isnan isnormal isunordered labs ldexp ldexpf ldexpl ldiv lgamma lgammaf lgammal llabs lldiv llrint llrintf llrintl llround llroundf llroundl log log10 log10f log10l log1p log1pf log1pl log2 log2f log2l logb logbf logbl logf logl lrint lrintf lrintl lround lroundf lroundl MATH_ERREXCEPT math_errhandling MATH_ERRNO modf modff modfl nan NAN nanf nanl nearbyint nearbyintf nearbyintl nextafter nextafterf nextafterl nexttoward nexttowardf nexttowardl Numerics pow powf powl Pseudo-random number generation rand RAND_MAX remainder remainderf remainderl remquo remquof remquol rint rintf rintl round roundf roundl scalbln scalblnf scalblnl scalbn scalbnf scalbnl signbit sin sinf sinh sinhf sinhl sinl sqrt sqrtf sqrtl srand tan tanf tanh tanhf tanhl tanl tgamma tgammaf tgammal trunc truncf truncl Type-generic math _Complex_I _Imaginary_I Program support abort atexit at_quick_exit exit EXIT_FAILURE EXIT_SUCCESS getenv getenv_s jmp_buf longjmp Program support utilities quick_exit raise setjmp SIGABRT SIGFPE SIGILL SIGINT signal SIGSEGV SIGTERM sig_atomic_t SIG_DFL SIG_ERR SIG_IGN system _Exit Strings atof atoi atol atoll btowc c16rtomb c32rtomb char16_t char32_t isalnum isalpha isblank iscntrl isdigit isgraph islower isprint ispunct isspace isupper iswalnum iswalpha iswblank iswcntrl iswctype iswdigit iswgraph iswlower iswprint iswpunct iswspace iswupper iswxdigit isxdigit mblen mbrlen mbrtoc16 mbrtoc32 mbrtowc mbsinit mbsrtowcs mbsrtowcs_s mbstate_t mbstowcs mbstowcs_s mbtowc memchr memcmp memcpy memcpy_s memmove memmove_s memset memset_s Null-terminated byte strings Null-terminated multibyte strings Null-terminated wide strings strcat strcat_s strchr strcmp strcoll strcpy strcpy_s strcspn strerror strerrorlen_s strerror_s Strings library strlen strncat Thread support call_once cnd_broadcast cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait mtx_destroy mtx_init mtx_lock mtx_plain mtx_recursive mtx_timed mtx_timedlock mtx_trylock mtx_unlock once_flag ONCE_FLAG_INIT thrd_busy thrd_create thrd_current thrd_detach thrd_equal thrd_error thrd_exit thrd_join thrd_nomem thrd_sleep thrd_success thrd_timedout thrd_yield Thread support library thread_local tss_create tss_delete TSS_DTOR_ITERATIONS tss_get tss_set Type support Boolean type support library Fixed width integer types FLT_EVAL_METHOD FLT_ROUNDS max_align_t NULL Numeric limits offsetof ptrdiff_t size_t Type support Variadic functions Variadic functions va_arg va_copy va_end va_list va_start
characters

句法

_Atomic ( type-name )

(1)

(since C11)

_Atomic type-name

(2)

(since C11)

1)用作類型說明符; 這指定了一種新的原子類型

2)用作類型限定詞; 這指定了類型名稱的原子版本。在這個角色中,它可能與 const,volatile 和 restrict混合使用),但與其他限定符不同,type-name 的原子版本可能具有不同的大小,對齊和對象表示。

type-name

-

any type other than array or function. For (1), type-name also cannot be atomic or cvr-qualified

<stdatomic.h>定義37層便于使用的宏,從atomic_boolatomic_uintmax_t,這簡化使用這個關(guān)鍵字與內(nèi)置和庫類型的。

_Atomic const int * p1;  // p is a pointer to an atomic const intconst atomic_int * p2;   // sameconst _Atomic(int) * p3; // same

說明

原子類型的對象是唯一沒有數(shù)據(jù)競爭的對象,也就是說,它們可以被兩個線程同時修改或修改一個并被另一個線程修改。

每個原子對象都有自己的關(guān)聯(lián)修改順序,這是對該對象進(jìn)行修改的總順序。如果從某個線程的角度來看,A某些原子M的修改發(fā)生在修改B相同的原子 M 之前,那么按M的修改順序,A 在 B 之前發(fā)生。

請注意,雖然每個原子對象都有自己的修改順序,但它不是總順序; 不同的線程可以觀察對不同順序的不同原子對象的修改。

所有原子操作都有四種連貫性保證:

  • 寫 - 寫連貫性:如果修改原子對象M的操作A 發(fā)生在修改M的操作B 之前,則A按修改順序M出現(xiàn)在B之前。

  • 讀讀連貫性:如果原子對象M的值計算A在M的值計算B之前發(fā)生,并且A從M上的副作用X取其值,并且由B計算的值是由X存儲的值或者是由M上的副作用Y存儲的值,其中Y以M的修改順序比X晚出現(xiàn)。

  • 讀寫連貫性:如果原子對象M的值計算A在M上的操作B 之前發(fā)生,則A從M上的副作用X取其值,其中X以B的修改順序出現(xiàn)在M之前。

  • 寫讀連貫性:如果原子對象M上的副作用X 發(fā)生在 M 的值計算B 之前,則評估B從X或從修飾順序為M的X之后出現(xiàn)的副作用Y中獲取其值。

一些原子操作也是同步操作; 他們可能會有額外的釋放語義,獲取語義或順序一致的語義???code>memory_order。

內(nèi)置增量和減量運算符和復(fù)合賦值是按順序一致的順序進(jìn)行讀 - 修改 - 寫原子操作(就像使用一樣memory_order_seq_cst)。如果需要較不嚴(yán)格的同步語義,則可以使用標(biāo)準(zhǔn)庫函數(shù)。

原子屬性只對左值表達(dá)式有意義。左值到右值轉(zhuǎn)換(將從原子位置讀到CPU寄存器的內(nèi)存建模)與其他限定符一起剝離原子性。

筆記

如果宏常量__STDC_NO_ATOMICS__(C11)由編譯器定義,則不提供關(guān)鍵字_Atomic和標(biāo)題<stdatomic.h>。

訪問原子結(jié)構(gòu)/聯(lián)合的成員是未定義的行為。

庫類型sig_atomic_t不提供線程間同步或內(nèi)存排序,只有原子性。

易失性類型不提供線程間同步,內(nèi)存排序或原子性。

關(guān)鍵詞

_Atomic.

#include <stdio.h>#include <threads.h>#include <stdatomic.h>
 atomic_int acnt;int cnt;
 int f(void* thr_data){    for(int n = 0; n < 1000; ++n) {        ++cnt;        ++acnt;        // for this example, relaxed memory order is sufficient, e.g.        // atomic_fetch_add_explicit(&acnt, 1, memory_order_relaxed);    }    return 0;}
 int main(void){
    thrd_t thr[10];    for(int n = 0; n < 10; ++n)        thrd_create(&thr[n], f, NULL);    for(int n = 0; n < 10; ++n)        thrd_join(thr[n], NULL); 
    printf("The atomic counter is %u\n", acnt);    printf("The non-atomic counter is %u\n", cnt);}

可能的輸出:

The atomic counter is 10000The non-atomic counter is 8644
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