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Identifiers reserved for functions names are always {{rev inl|since=c23|potentially}} reserved for use as identifiers with external linkage, while other identifiers list here are {{rev inl|since=c23|potentially}} reserved when {{tt|<stdatomic.h>}} is included.
 
Identifiers reserved for functions names are always {{rev inl|since=c23|potentially}} reserved for use as identifiers with external linkage, while other identifiers list here are {{rev inl|since=c23|potentially}} reserved when {{tt|<stdatomic.h>}} is included.
  
−
Declaring, defining, or {{c|#undef}}ing such an identifier results in undefined behavior{{rev inl|since=c23|if it is provided by the standard or implementation}}. Portable programs should not use those identifiers.
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Declaring, defining, or {{c|#undef}}ing such an identifier results in undefined behavior{{rev inl|since=c23| if it is provided by the standard or implementation}}. Portable programs should not use those identifiers.
  
 
===References===
 
===References===

Revision as of 17:14, 14 July 2023

 
C
 
Concurrency support library
 

C includes built-in support for threads, atomic operations, mutual exclusion, condition variables, and thread-specific storages.

These features are optionally provided:

  • if the macro constant __STDC_NO_THREADS__ is defined by the compiler, the header <threads.h> and all of the names provided in it are not provided;
  • if the macro constant __STDC_NO_ATOMICS__ is defined by the compiler, the header <stdatomic.h> and all of the names provided in it are not provided.

Contents

Threads

Defined in header <threads.h>
thrd_t implementation-defined complete object type identifying a thread [edit]
(C11)
 creates a thread
(function) [edit]
(C11)
 checks if two identifiers refer to the same thread
(function) [edit]
(C11)
 obtains the current thread identifier
(function) [edit]
(C11)
 suspends execution of the calling thread for the given period of time
(function) [edit]
(C11)
 yields the current time slice
(function) [edit]
(C11)
 terminates the calling thread
(function) [edit]
(C11)
 detaches a thread
(function) [edit]
(C11)
 blocks until a thread terminates
(function) [edit]
(C11)
 indicates a thread error status
(constant) [edit]
thrd_start_t
(C11)
 a typedef of the function pointer type int(*)(void*), used by thrd_create
(typedef) [edit]

Atomic operations

Defined in header <stdatomic.h>
Operations on atomic types
(C11)
 indicates that the given atomic type is lock-free
(macro constant) [edit]
(C11)
 indicates whether the atomic object is lock-free
(function) [edit]
(C11)
 stores a value in an atomic object
(function) [edit]
(C11)
 reads a value from an atomic object
(function) [edit]
(C11)
 swaps a value with the value of an atomic object
(function) [edit]
(C11)
 swaps a value with an atomic object if the old value is what is expected, otherwise reads the old value
(function) [edit]
(C11)
 atomic addition
(function) [edit]
(C11)
 atomic subtraction
(function) [edit]
(C11)
 atomic bitwise OR
(function) [edit]
(C11)
 atomic bitwise exclusive OR
(function) [edit]
(C11)
 atomic bitwise AND
(function) [edit]
Flag type and operations
(C11)
 lock-free atomic boolean flag
(struct)[edit]
(C11)
 sets an atomic_flag to true and returns the old value
(function) [edit]
(C11)
 sets an atomic_flag to false
(function) [edit]
Initialization
(C11)
 initializes an existing atomic object
(function) [edit]
(C11)(deprecated in C17)(removed in C23)
 initializes a new atomic object
(function macro) [edit]
(C11)
 initializes a new atomic_flag
(macro constant) [edit]
Memory synchronization ordering
(C11)
 defines memory ordering constraints
(enum) [edit]
(C11)
 breaks a dependency chain for memory_order_consume
(function macro) [edit]
(C11)
 generic memory order-dependent fence synchronization primitive
(function) [edit]
(C11)
 fence between a thread and a signal handler executed in the same thread
(function) [edit]
Convenience type aliases
Typedef name Full type name
atomic_bool(C11) _Atomic _Bool
atomic_char(C11) _Atomic char
atomic_schar(C11) _Atomic signed char
atomic_uchar(C11) _Atomic unsigned char
atomic_short(C11) _Atomic short
atomic_ushort(C11) _Atomic unsigned short
atomic_int(C11) _Atomic int
atomic_uint(C11) _Atomic unsigned int
atomic_long(C11) _Atomic long
atomic_ulong(C11) _Atomic unsigned long
atomic_llong(C11) _Atomic long long
atomic_ullong(C11) _Atomic unsigned long long
atomic_char8_t(C23) _Atomic char8_t
atomic_char16_t(C11) _Atomic char16_t
atomic_char32_t(C11) _Atomic char32_t
atomic_wchar_t(C11) _Atomic wchar_t
atomic_int_least8_t(C11) _Atomic int_least8_t
atomic_uint_least8_t(C11) _Atomic uint_least8_t
atomic_int_least16_t(C11) _Atomic int_least16_t
atomic_uint_least16_t(C11) _Atomic uint_least16_t
atomic_int_least32_t(C11) _Atomic int_least32_t
atomic_uint_least32_t(C11) _Atomic uint_least32_t
atomic_int_least64_t(C11) _Atomic int_least64_t
atomic_uint_least64_t(C11) _Atomic uint_least64_t
atomic_int_fast8_t(C11) _Atomic int_fast8_t
atomic_uint_fast8_t(C11) _Atomic uint_fast8_t
atomic_int_fast16_t(C11) _Atomic int_fast16_t
atomic_uint_fast16_t(C11) _Atomic uint_fast16_t
atomic_int_fast32_t(C11) _Atomic int_fast32_t
atomic_uint_fast32_t(C11) _Atomic uint_fast32_t
atomic_int_fast64_t(C11) _Atomic int_fast64_t
atomic_uint_fast64_t(C11) _Atomic uint_fast64_t
atomic_intptr_t(C11) _Atomic intptr_t
atomic_uintptr_t(C11) _Atomic uintptr_t
atomic_size_t(C11) _Atomic size_t
atomic_ptrdiff_t(C11) _Atomic ptrdiff_t
atomic_intmax_t(C11) _Atomic intmax_t
atomic_uintmax_t(C11) _Atomic uintmax_t

Mutual exclusion

Defined in header <threads.h>
mtx_t mutex identifier [edit]
(C11)
 creates a mutex
(function) [edit]
(C11)
 blocks until locks a mutex
(function) [edit]
(C11)
 blocks until locks a mutex or times out
(function) [edit]
(C11)
 locks a mutex or returns without blocking if already locked
(function) [edit]
(C11)
 unlocks a mutex
(function) [edit]
(C11)
 destroys a mutex
(function) [edit]
(C11)(C11)(C11)
 defines the type of a mutex
(enum) [edit]
Call once
(C11)
 calls a function exactly once
(function) [edit]

Condition variables

Defined in header <threads.h>
cnd_t condition variable identifier
(C11)
 creates a condition variable
(function) [edit]
(C11)
 unblocks one thread blocked on a condition variable
(function) [edit]
(C11)
 unblocks all threads blocked on a condition variable
(function) [edit]
(C11)
 blocks on a condition variable
(function) [edit]
(C11)
 blocks on a condition variable, with a timeout
(function) [edit]
(C11)
 destroys a condition variable
(function) [edit]

Thread-local storage

Defined in header <threads.h>
(C11)(removed in C23)
 convenience macro for storage-class specifier _Thread_local
(keyword macro) [edit]
tss_t thread-specific storage pointer [edit]
(C11)
 maximum number of times destructors are called
(macro constant) [edit]
tss_dtor_t
(C11)
 function pointer type void(*)(void*), used for TSS destructor
(typedef) [edit]
(C11)
 creates thread-specific storage pointer with a given destructor
(function) [edit]
(C11)
 reads from thread-specific storage
(function) [edit]
(C11)
 write to thread-specific storage
(function) [edit]
(C11)
 releases the resources held by a given thread-specific pointer
(function) [edit]

Reserved identifiers

In future revisions of the C standard:

  • function names, type names, and enumeration constants that begin with either cnd_, mtx_, thrd_, or tss_, and a lowercase letter may be added to the declarations in the <threads.h> header;
  • macros that begin with ATOMIC_ and an uppercase letter may be added to the macros defined in the <stdatomic.h> header;
  • typedef names that begin with either atomic_ or memory_, and a lowercase letter may be added to the declarations in the <stdatomic.h> header;
  • enumeration constants that begin with memory_order_ and a lowercase letter may be added to the definition of the memory_order type in the <stdatomic.h> header;
  • function names that begin with atomic_ and a lowercase letter may be added to the declarations in the <stdatomic.h> header.

Identifiers reserved for functions names are always potentially(since C23) reserved for use as identifiers with external linkage, while other identifiers list here are potentially(since C23) reserved when <stdatomic.h> is included.

Declaring, defining, or #undefing such an identifier results in undefined behavior if it is provided by the standard or implementation(since C23). Portable programs should not use those identifiers.

References

  • C23 standard (ISO/IEC 9899:2024):
  • C17 standard (ISO/IEC 9899:2018):
  • 7.17 Atomics <stdatomic.h> (p: 200-209)
  • 7.26 Threads <threads.h> (p: 274-283)
  • 7.31.8 Atomics <stdatomic.h> (p: 332)
  • 7.31.15 Threads <threads.h> (p: 333)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.17 Atomics <stdatomic.h> (p: 273-286)
  • 7.26 Threads <threads.h> (p: 376-387)
  • 7.31.8 Atomics <stdatomic.h> (p: 455-456)
  • 7.31.15 Threads <threads.h> (p: 456)

See also

C++ documentation for Concurrency support library

External links

GNU GCC Libc Manual: ISO C Mutexes
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