elisp: Accepting Output
36.9.4 Accepting Output from Processes
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Output from asynchronous subprocesses normally arrives only while Emacs
is waiting for some sort of external event, such as elapsed time or
terminal input. Occasionally it is useful in a Lisp program to
explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.
-- Function: accept-process-output &optional process seconds millisec
just-this-one
This function allows Emacs to read pending output from processes.
The output is given to their filter functions. If PROCESS is
non-‘nil’ then this function does not return until some output has
been received from PROCESS.
The arguments SECONDS and MILLISEC let you specify timeout periods.
The former specifies a period measured in seconds and the latter
specifies one measured in milliseconds. The two time periods thus
specified are added together, and ‘accept-process-output’ returns
after that much time, even if there is no subprocess output.
The argument MILLISEC is obsolete (and should not be used), because
SECONDS can be floating point to specify waiting a fractional
number of seconds. If SECONDS is 0, the function accepts whatever
output is pending but does not wait.
If PROCESS is a process, and the argument JUST-THIS-ONE is
non-‘nil’, only output from that process is handled, suspending
output from other processes until some output has been received
from that process or the timeout expires. If JUST-THIS-ONE is an
integer, also inhibit running timers. This feature is generally
not recommended, but may be necessary for specific applications,
such as speech synthesis.
The function ‘accept-process-output’ returns non-‘nil’ if it got
output from PROCESS, or from any process if PROCESS is ‘nil’. It
returns ‘nil’ if the timeout expired before output arrived.
Info Catalog
elisp: Decoding Output
elisp: Output from Processes