Built-in atomic operation functions of GCC

Recently, in the user State, we suddenly needed to use atomic variables, and didn't want to compile boost on our own. We accidentally found that GCC still has this set of built-in functions.

// First perform the operation, and then return the changed Value Type _ sync_fetch_and_add (type * PTR, type value); Type _ sync_fetch_and_sub (type * PTR, type value ); type _ sync_fetch_and_or (type * PTR, type value); Type _ sync_fetch_and_and (type * PTR, type value); Type _ sync_fetch_and_xor (type * PTR, type value ); type _ sync_fetch_and_nand (type * PTR, type value); // first return the value before the change, and then perform the operation type _ sync_add_and_fetch (type * PTR, type value ); type _ sync_sub_and_fetch (type * PTR, type value); Type _ sync_or_and_fetch (type * PTR, type value); Type _ sync_and_and_fetch (type * PTR, type value ); type _ sync_xor_and_fetch (type * PTR, type value); Type _ sync_nand_and_fetch (type * PTR, type value );

According to the official document,

GCC will allow any integral scalar or pointer type that is 1, 2, 4, or 8 bytes in length. 16-byte integral types are also allowed if '_ int128' (see _ int128) is supported by the architecture.

That is to say, an integer with a length of at least 1, 2, and 4, 8 is supported.

After a simple test, we found that no header files need to be included. During GCC compilation, the corresponding assembly code is automatically replaced.

int main(){    int a = 100;    __sync_fetch_and_add(&a,1);    return a;}

The following figure shows the generated assembly:

. File "funtest. C ". text. globl main. type main, @ functionmain :. lfb0 :. cfi_startproc pushq % RBP. cfi_def_cfa_offset 16. cfi_offset 6,-16 movq % RSP, % RBP. cfi_def_cfa_register 6 movl $100,-4 (% RBP) Lock addl $1,-4 (% RBP) // _ sync_fetch_and_add (& A, 1 ); corresponding command movl-4 (% RBP), % eax popq % RBP. cfi_def_cfa 7, 8 ret. cfi_endproc.lfe0 :. size main ,. -Main. ident "GCC: (Debian 4.7.2-5) 4.7.2 ". section. note. GNU-stack, "", @ progbits

Reference

Https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/_005f_005fatomic-Builtins.html#_005f_005fatomic-Builtins

Built-in atomic operation functions of GCC