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Improve documentation around standard error pipes (Bug#35328).

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* doc/lispref/processes.texi (Asynchronous Processes): Document
existence and properties of the standard error process.
(Accepting Output): Document that one has to accept output from the
standard error process separately.
This commit is contained in:
Philipp Stephani 2019-04-21 18:09:38 +02:00
parent f9659e648c
commit 3b4e312cfe
1 changed files with 26 additions and 0 deletions
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doc/lispref/processes.texi
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@ -701,6 +701,19 @@ created with @code{make-pipe-process}, described below. If
@var{stderr} is @code{nil}, standard error is mixed with standard
output, and both are sent to @var{buffer} or @var{filter}.
@cindex standard error process
If @var{stderr} is a buffer, Emacs will create a pipe process, the
@dfn{standard error process}. This process will have the default
filter (@pxref{Filter Functions}), sentinel (@pxref{Sentinels}), and
coding systems (@pxref{Default Coding Systems}). On the other hand,
it will use @var{query-flag} as its query-on-exit flag (@pxref{Query
Before Exit}). It will be associated with the @var{stderr} buffer
(@pxref{Process Buffers}) and send its output (which is the standard
error of the main process) there.
If @var{stderr} is a pipe process, Emacs will use it as standard error
process for the new process.
@item :file-handler @var{file-handler}
If @var{file-handler} is non-@code{nil}, then look for a file name
handler for the current buffer's @code{default-directory}, and invoke
@ -1882,6 +1895,19 @@ like this:
(while (accept-process-output process))
@end example
If you have passed a non-@code{nil} @var{stderr} to
@code{make-process}, it will have a standard error process.
@xref{Asynchronous Processes}. In that case, waiting for process
output from the main process doesn't wait for output from the standard
error process. To make sure you have received both all of standard
output and all of standard error from a process, use the following
code:
@example
(while (accept-process-output process))
(while (accept-process-output stderr-process))
@end example
@node Processes and Threads
@subsection Processes and Threads
@cindex processes, threads