/usr/local/lib/swipl/library/ext/clib/process.pl
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 process_wait(+PID, -Status) is det
 process_wait(+PID, -Status, +Options) is det
True if PID completed with Status. This call normally blocks until the process is finished. Options:
timeout(+Timeout)
Default: infinite. If this option is a number, the waits for a maximum of Timeout seconds and unifies Status with timeout if the process does not terminate within Timeout. In this case PID is not invalidated. On Unix systems only timeout 0 and infinite are supported. A 0-value can be used to poll the status of the process.
release(+Bool)
Do/do not release the process. We do not support this flag and a domain_error is raised if release(false) is provided.
Arguments:
Status- is one of exit(Code) or killed(Signal), where Code and Signal are integers. If the timeout option is used Status is unified with timeout after the wait timed out.