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Improve documentation of 'process-connection-type'

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* doc/lispref/processes.texi (Asynchronous Processes): Clarify
better when it is advisable to use pipes for communicating
with subprocesses.  (Bug#33050)
This commit is contained in:
Eli Zaretskii 2018-10-27 13:18:33 +03:00
parent 106b9e138f
commit 9193db08de
1 changed files with 12 additions and 7 deletions
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doc/lispref/processes.texi
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@ -590,8 +590,8 @@ communication is only partially asynchronous: Emacs sends data to the
process only when certain functions are called, and Emacs accepts data
from the process only while waiting for input or for a time delay.
@cindex pty
@cindex pipe
@cindex pty, when to use for subprocess communications
@cindex pipe, when to use for subprocess communications
An asynchronous process is controlled either via a @dfn{pty}
(pseudo-terminal) or a @dfn{pipe}. The choice of pty or pipe is made
when creating the process, by default based on the value of the
@ -601,11 +601,13 @@ Shell mode, because they allow for job control (@kbd{C-c}, @kbd{C-z},
etc.)@: between the process and its children, and because interactive
programs treat ptys as terminal devices, whereas pipes don't support
these features. However, for subprocesses used by Lisp programs for
internal purposes, it is often better to use a pipe, because pipes are
internal purposes (i.e., with no user interaction), where significant
amounts of data need to be exchanged between the subprocess and the
Lisp program, it is often better to use a pipe, because pipes are
more efficient, and because they are immune to stray character
injections that ptys introduce for large (around 500 byte) messages.
Also, the total number of ptys is limited on many systems and it is
good not to waste them.
Also, the total number of ptys is limited on many systems, and it is
good not to waste them unnecessarily.
@defun make-process &rest args
This function is the basic low-level primitive for starting
@ -658,7 +660,9 @@ pipe, or @code{nil} to use the default derived from the value of the
@code{process-connection-type} variable. This parameter and the value
of @code{process-connection-type} are ignored if a non-@code{nil}
value is specified for the @code{:stderr} parameter; in that case, the
type will always be @code{pipe}.
type will always be @code{pipe}. On systems where ptys are not
available (MS-Windows), this parameter is likewise ignored, and pipes
are used unconditionally.
@item :noquery @var{query-flag}
Initialize the process query flag to @var{query-flag}.
@ -863,7 +867,8 @@ around the call to these functions.
Note that the value of this variable is ignored when
@code{make-process} is called with a non-@code{nil} value of the
@code{:stderr} parameter; in that case, Emacs will communicate with
the process using pipes.
the process using pipes. It is also ignored if ptys are unavailable
(MS-Windows).
@smallexample
@group