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'\" te .\" Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved. .TH membar_ops 3C "14 Feb 2005" "Oracle Solaris 11.4" "Standard C Library Functions" .SH NAME membar_ops, membar_enter, membar_exit, membar_producer, membar_consumer \- memory access synchronization barrier operations .SH SYNOPSIS .LP .nf #include <atomic.h> \fBvoid\fR \fBmembar_enter\fR(\fBvoid\fR); .fi .LP .nf \fBvoid\fR \fBmembar_exit\fR(\fBvoid\fR); .fi .LP .nf \fBvoid\fR \fBmembar_producer\fR(\fBvoid\fR); .fi .LP .nf \fBvoid\fR \fBmembar_consumer\fR(\fBvoid\fR); .fi .SH DESCRIPTION .sp .LP The \fBmembar_enter()\fR function is a generic memory barrier used during lock entry. It is placed after the memory operation that acquires the lock to guarantee that the lock protects its data. No stores from after the memory barrier will reach visibility and no loads from after the barrier will be resolved before the lock acquisition reaches global visibility. .sp .LP The \fBmembar_exit()\fR function is a generic memory barrier used during lock exit. It is placed before the memory operation that releases the lock to guarantee that the lock protects its data. All loads and stores issued before the barrier will be resolved before the subsequent lock update reaches visibility. .sp .LP The \fBmembar_enter()\fR and \fBmembar_exit()\fR functions are used together to allow regions of code to be in relaxed store order and then ensure that the load or store order is maintained at a higher level. They are useful in the implementation of mutex exclusion locks. .sp .LP The \fBmembar_producer()\fR function arranges for all stores issued before this point in the code to reach global visibility before any stores that follow. This is useful in producer modules that update a data item, then set a flag that it is available. The memory barrier guarantees that the available flag is not visible earlier than the updated data, thereby imposing store ordering. .sp .LP The \fBmembar_consumer()\fR function arranges for all loads issued before this point in the code to be completed before any subsequent loads. This is useful in consumer modules that check if data is available and read the data. The memory barrier guarantees that the data is not sampled until after the available flag has been seen, thereby imposing load ordering. .SH RETURN VALUES .sp .LP No values are returned. .SH ERRORS .sp .LP No errors are defined. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(7) for descriptions of the following attributes: .sp .TS tab( ) box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Committed _ MT-Level MT-Safe .TE .sp .SH SEE ALSO .sp .LP \fBatomic_add\fR(3C), \fBatomic_and\fR(3C), \fBatomic_bits\fR(3C), \fBatomic_cas\fR(3C), \fBatomic_dec\fR(3C), \fBatomic_inc\fR(3C), \fBatomic_ops\fR(3C), \fBatomic_or\fR(3C), \fBatomic_swap\fR(3C), \fBattributes\fR(7), \fBatomic_ops\fR(9F) .SH NOTES .sp .LP Atomic instructions (see \fBatomic_ops\fR(3C)) ensure global visibility of atomically-modified variables on completion. In a relaxed store order system, this does not guarantee that the visibility of other variables will be synchronized with the completion of the atomic instruction. If such synchronization is required, memory barrier instructions must be used.