Special mechanism for making sure forms execute in the main thread.
This is a special form that is only meant to be used by ACL2 Bridge clients when they issue commands. A syntax example is:
(bridge::in-main-thread (memoize 'fib) (fib 37))
This is really just a hack that lets you use commands that, for one reason or another, must only ever be executed in the "main" thread (in CCL parlance, the "initial listener" thread). Practical applications include:
If the main thread is busy with work from other clients, this form will wait until it becomes available again. See also try-in-main-thread, which instead just causes an error if the main thread is busy.