Parallel Programming Guide for HP-UX Systems

Parallel synchronization

Synchronization tools

Chapter 8146

The forms of these directives and pragmas are shown in Table 8-8.

where

gate

is an optional gate variable used for access to the

critical section.

gate

must be appropriately declared as

described in the “Using gates and barriers” on

page 136.

The gate variable is required when synchronizing access to a shared

variable from multiple parallel tasks.

• When a gate variable is speciﬁed, it must be allocated (using the

alloc_gate intrinsic) outside of parallel code prior to use

• If no gate is speciﬁed, the compiler creates a unique gate for the

critical section

• When a gate is no longer needed, it should be deallocated using the

free_gate function.

NOTE Critical sections add synchronization overhead to your

program. They should only be used when the amount of

parallel code is signiﬁcantly larger than the amount of

code containing the dependence.

Table 8-8 Forms of critical_section, end_critical_section

directives and pragmas

Language Form

Fortran C$DIR CRITICAL_SECTION[(gate)]

...

C$DIR END_CRITICAL_SECTION

C #pragma _CNX

critical_section[(gate)] ...#pragma

_CNX end_critical_section