LOCK Statement

General Format

LOCK THREAD

General Rules

1. The LOCK THREAD statement prevents other threads from running. The thread that executes the LOCK statement is the only thread allowed to run until an UNLOCK THREAD statement is executed, or the thread terminates. Locking a thread ensures that other threads will not modify a critical piece of data or other shared resource.
2. A thread can be locked multiple times. Each time a thread executes a LOCK THREAD statement, the number of locks held by the thread increases by one. In order to unlock a thread with multiple locks, an equal number of UNLOCK THREAD statements must execute.

   This allows a thread to lock itself, call a subroutine that also locks itself, and remain locked when that subroutines unlocks itself. See UNLOCK THREAD.