$RELEASE

$RELEASE function

General Form:

$RELEASE

Valid wherever a numeric expression is valid.

The $RELEASE function is used to clone the existing program and run it as a child process. The original program is suspended and its entire environment is unaffected by anything that might occur in the clone copy. The main use of this function is to allow the running of a second program which might destroy the value of common variables or overwrite program lines.

The parent process will be suspended until the child terminates by executing $END. The parent then receives the argument of the $END and returns it as the value of the $RELEASE function. The child always returns -1 as its value for the function and so the program can tell whether it is executing in the parents copy (>= 0) or the childs copy (-1). If however the cloning operation fails, perhaps because some resource such as paging space is unavailable, the function may return -2. This indicates that there is still only one partition and the application should give an error.

The Unix implementation of $RELEASE uses the fork system call to create a second duplicate process with a different process ID as well as a different partition number #PART. Microsoft Windows does not support fork so the second partition is created inside the context of the original process. It has a different #PART value but shares the same process ID.

While the parent process is blocked waiting on the child terminating its terminal status in $PSTAT is set to 'F'. To avoid double counting in the Windows implementation the memory page count in $PSTAT is set to zero for the parent while the child is active.

Byte 63 of $MACHINE can be inspected to check $RELEASE status. The bottom 7 bits of this byte is incremented in a $RELEASE child process. It will be zero outside of a $RELEASE, 1 while executing in a $RELEASE child and perhaps 2 if the process is the child of a $RELEASE executed inside a $RELEASE child. The HEX(80) bit of the byte is set in the parent on return from a $RELEASE as a marker that at least one $RELEASE was performed by this process.

In the following example the child partition is started when the $RELEASE function is executed. Control is returned to the parent partition when the child executes a $END statement.

SELECT CASE $RELEASE
CASE -1
    REM Now executing in the child copy
    COM CLEAR fred$
    LOAD "PROGONE" 1000
CASE -2
    REM fatal error
    PANIC
CASE ELSE
    REM Executing parent with child terminated
        ...
END SELECT

Syntax examples:

test = $RELEASE + 1
PRINT $RELEASE
IF ($RELEASE == -2)

Compatibility: AIX versions of KCML 6.90 (or later) must not run with the $KCML_SHARED_HEAP environment variable set.
The child partition must not use an secure socket that was opened by the parent.