Open Watcom FORTRAN 77 Language Reference

Language Reference
2.82 VOLATILE Statement
VOLATILE [a [,a] ...]
where:
a
is a variable name or an array name.
The VOLATILE statement is used to indicate that a variable or an element of an array may be updated
concurrently by other code. A volatile variable or array element will not be cached (in a register) by the
code generator. Each time a volatile variable or array element is referenced, it is loaded from memory.
Each time a volatile variable or array element is updated, it is stored back into memory.
Notes:
1. A name cannot appear in a VOLATILE statement more than once in the same program unit.
2. Dummy arguments, procedure names, and common block names are not permitted in a
VOLATILE statement.
In the following example, the subroutine A_THREAD waits on the HoldThreads semaphore. It uses the
VOLATILE statement to ensure that the variable is re-loaded from memory each time through the loop.
Example:
SUBROUTINE A_THREAD()
STRUCTURE /RTL_CRITICAL_SECTION/
INTEGER*4 DebugInfo
INTEGER*4 LockCount
INTEGER*4 RecursionCount
INTEGER*4 OwningThread
INTEGER*4 LockSemaphore
INTEGER*4 Reserved
END STRUCTURE
INTEGER NumThreads
LOGICAL HoldThreads
VOLATILE HoldThreads
RECORD /RTL_CRITICAL_SECTION/ CriticalSection
COMMON NumThreads, HoldThreads, CriticalSection
INTEGER threadid
WHILE( HoldThreads )DO
CALL Sleep( 1 )
END WHILE
PRINT ’(’’Hi from thread ’’, i4)’, threadid()
CALL EnterCriticalSection( CriticalSection )
NumThreads = NumThreads - 1
CALL LeaveCriticalSection( CriticalSection )
CALL endthread()
END
144 VOLATILE Statement