MEMBARRIER(2) System Calls Manual MEMBARRIER(2) NAME membarrier -- memory barrier LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <sys/membarrier.h> int membarrier(int cmd, unsigned flags, int cpu_id); DESCRIPTION The membarrier system call provides a memory barrier, ensuring ordering be- tween memory accesses performed by different threads or processes within the same address space. The following values for cmd may be specified: MEMBARRIER_CMD_QUERY Query supported commands. A bitmask of commands supported by the kernel is returned. MEMBARRIER_CMD_GLOBAL Issue a memory barrier for all threads from all processes. MEMBARRIER_CMD_SHARED This is an alias for MEMBARRIER_CMD_GLOBAL. MEMBARRIER_CMD_GLOBAL_EXPEDITED Execute a memory barrier on all running threads of all processes registered with MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED. MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED Register the process to receive MEMBARRIER_CMD_GLOBAL_EXPEDITED memory barriers. MEMBARRIER_CMD_PRIVATE_EXPEDITED Execute a memory barrier on each running thread belonging to the same process as the thread calling membarrier. MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED Register the process to receive MEMBARRIER_CMD_PRIVATE_EXPEDITED memory barriers. MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE In addition to the guarantees provided by MEMBARRIER_CMD_PRIVATE_EXPEDITED it also executes machine- specific serialization instructions, which ensures that all possible speculative and out-of-order activities on the tar- get CPU are fenced. MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE Register the process to receive MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE memory barriers. MEMBARRIER_CMD_GET_REGISTRATIONS Return the bitmask of the currently registered receive barri- ers. The following cmd values are defined for source compatibility but are not yet supported: MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ The flags argument must be 0. The cpu_id argument is ignored. RETURN VALUES If the cmd is MEMBARRIER_CMD_QUERY a bitmask of supported commands is re- turned. For the MEMBARRIER_CMD_GET_REGISTRATIONS command, a bitmask of the registrations for the current process is returned. Otherwise, on success, membarrier returns 0. On error, -1 is returned and errno is set to indi- cate the error. ERRORS membarrier may fail with the following errors: [EINVAL] cmd does not specify a valid command. [EINVAL] flags is not 0. [EPERM] An attempt was made to use MEMBARRIER_CMD_GLOBAL_EXPEDITED, MEMBARRIER_CMD_PRIVATE_EXPEDITED, or MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE by a process that did not previously register use with the corre- sponding MEMBARRIER_CMD_REGISTER_* cmd. STANDARDS The membarrier system call originated in Linux. This implementation aims to be source-compatible with the Linux implementation. Certain cmd and flags values are currently not supported by FreeBSD. HISTORY The membarrier function was introduced in FreeBSD 14.1. FreeBSD 15.1 October 6, 2024 MEMBARRIER(2)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | STANDARDS | HISTORY
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