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38.9.5 Processes and Threads

Because threads were a relatively late addition to Emacs Lisp, and due to the way dynamic binding was sometimes used in conjunction with accept-process-output, by default a process is locked to the thread that created it. When a process is locked to a thread, output from the process can only be accepted by that thread.

A Lisp program can specify to which thread a process is to be locked, or instruct Emacs to unlock a process, in which case its output can be processed by any thread. Only a single thread will wait for output from a given process at one time—once one thread begins waiting for output, the process is temporarily locked until accept-process-output or sit-for returns.

If the thread exits, all the processes locked to it are unlocked.

Function: process-thread process

Return the thread to which process is locked. If process is unlocked, return nil.

Function: set-process-thread process thread

Set the locking thread of process to thread. thread may be nil, in which case the process is unlocked.