Rexx LOCK command: unspecified wait duration when NOWAIT omitted

Expected wait duration when LOCK is issued without NOWAIT

When the LOCK command is issued without the NOWAIT option, the Rexx program suspends execution until the requested file or region lock is granted by the operating system. Standard Rexx does not define a LOCK command; its behavior is implementation-specific and varies across Rexx interpreters and platforms. Consequently, no universal maximum wait duration is defined, and the suspension may last as long as another process holds the lock, potentially blocking backup or restore operations indefinitely.

Confirmed facts from the available research:

1. When NOWAIT is omitted, a blocking LOCK typically suspends the Rexx program until the lock is granted; no standard maximum wait duration is defined.
2. There is no standard Rexx mechanism to query or configure a blocking timeout for LOCK; any timeout depends on the underlying operating system or the specific Rexx implementation.
3. Restore or backup scripts that cannot tolerate indefinite suspension should use NOWAIT and handle the lock-unavailable case explicitly, or implement an external retry loop.
4. Some Rexx implementations may raise a condition or return an error when NOWAIT is specified and the lock is held, but the exact condition name and code are implementation-defined.

Practical recommendation for scripts that must complete within a known window:

1. Include the NOWAIT option in the LOCK command to ensure immediate return.
2. If the lock is unavailable, retry with a defined maximum number of attempts and a DELAY (or equivalent sleep) between attempts.
3. Capture the return code or condition raised when the lock fails to prevent the script from proceeding with an unsecured file.

Diagnostic requirement: To confirm whether a platform-specific timeout or query interface exists, please specify the Rexx interpreter and the host operating system.