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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
       between	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  sup-
		     ported 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  ma-
		     chine-specific serialization instructions,	which  ensures
		     that all possible speculative and out-of-order activities
		     on	the target CPU are fenced.

       MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE
		     Register	     the	process	      to       receive
		     MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE	memory	barri-
		     ers.

       MEMBARRIER_CMD_GET_REGISTRATIONS
		     Return  the  bitmask  of the currently registered receive
		     barriers.

       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
       returned.  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 indicate 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 corresponding 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	ports 15.quarterly	October	6, 2024			 MEMBARRIER(2)

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