# atomic_is_lock_free

< c‎ | atomic
 Defined in header  _Bool atomic_is_lock_free( const volatile A* obj ); (since C11)

Determines if the atomic operations on all objects of the type A (the type of the object pointed to by obj) are lock-free. In any given program execution, the result of calling atomic_is_lock_free is the same for all pointers of the same type.

This is a generic function defined for all atomic object types A. The argument is pointer to a volatile atomic type to accept addresses of both non-volatile and volatile (e.g. memory-mapped I/O) atomic objects, and volatile semantic is preserved when applying this operation to volatile atomic objects.

It is unspecified whether the name of a generic function is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual function (e.g. parenthesized like (atomic_is_lock_free)(...)), or a program defines an external identifier with the name of a generic function, the behavior is undefined.

## Contents

### Parameters

 obj - pointer to the atomic object to inspect

### Return value

true if the operations on all objects of the type A are lock-free, false otherwise.

### Notes

C11, as published, specified that this function is per-object, not per-type. This was corrected by DR 465.

### Example

#include <stdio.h>
#include <stdatomic.h>

_Atomic struct A { int a[100]; } a;
_Atomic struct B { int x, y; } b;
int main(void)
{
printf("_Atomic struct A is lock free? %s\n",
atomic_is_lock_free(&a) ? "true" : "false");
printf("_Atomic struct B is lock free? %s\n",
atomic_is_lock_free(&b) ? "true" : "false");
}

Possible output:

_Atomic struct A is lock free? false
_Atomic struct B is lock free? true

### References

• C11 standard (ISO/IEC 9899:2011):
• 7.17.5.1 The atomic_is_lock_free generic function (p: 280)