This option prevents simultaneous execution of two or more instances of the same task. While a task with SingleInstance option is being executed, no other instance of the same task cannot be started, and any attempt to start it will be suppressed.

In order to prevent a simultaneous execution of several different tasks (and two or more instances of the same task as well), one can use words GET и RELEASE. GET takes hold of a specified semaphore, and RELEASE releases it. These words use address of a variable (which is left on the stack after the variable has been used in the task) as their parameter. The succeeding tasks will be started, but they will be actually executed only after the preceding task releases the semaphore.