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Allow control of data amount read from subprocess in one chunk

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* src/process.c (syms_of_process) <read-process-output-max>:
New variable.
(read_process_output): Use it instead of the hard-coded
constant 4096.  (Bug#38561)
Use SAFE_ALLOCA to support large buffers for reading process
output.

* etc/NEWS: Mention 'read-process-output-max'.
This commit is contained in:
Eli Zaretskii 2019-12-21 10:47:31 +02:00
parent 0f7e3430bb
commit cc78faee7d
2 changed files with 22 additions and 5 deletions
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8
etc/NEWS
View file

@ -2724,6 +2724,14 @@ overlays. This is only done on 'display' properties that have the
** 'process-contact' now takes an optional NO-BLOCK argument to allow
not waiting for a process to be set up.
---
** New variable 'read-process-output-max' controls sub-process throughput.
This variable determines how many bytes can be read from a sub-process
in one read operation. The default, 4096 bytes, was previously a
hard-coded constant. Setting it to a larger value might enhance
throughput of reading from sub-processes that produces vast
(megabytes) amounts of data in one go.
+++
** The new user option 'quit-window-hook' is now run first when
executing the 'quit-window' command.

19
src/process.c
View file

@ -6008,7 +6008,7 @@ read_and_dispose_of_process_output (struct Lisp_Process *p, char *chars,
Yield number of decoded characters read,
or -1 (setting errno) if there is a read error.
This function reads at most 4096 characters.
This function reads at most read_process_output_max bytes.
If you want to read all available subprocess output,
you must call it repeatedly until it returns zero.
@ -6022,10 +6022,13 @@ read_process_output (Lisp_Object proc, int channel)
struct Lisp_Process *p = XPROCESS (proc);
struct coding_system *coding = proc_decode_coding_system[channel];
int carryover = p->decoding_carryover;
enum { readmax = 4096 };
ptrdiff_t readmax = clip_to_bounds (1, read_process_output_max, PTRDIFF_MAX);
ptrdiff_t count = SPECPDL_INDEX ();
Lisp_Object odeactivate;
char chars[sizeof coding->carryover + readmax];
char *chars;
USE_SAFE_ALLOCA;
chars = SAFE_ALLOCA (sizeof coding->carryover + readmax);
if (carryover)
/* See the comment above. */
@ -6092,7 +6095,7 @@ read_process_output (Lisp_Object proc, int channel)
if (nbytes <= 0)
{
if (nbytes < 0 || coding->mode & CODING_MODE_LAST_BLOCK)
return nbytes;
return SAFE_FREE_UNBIND_TO (count, nbytes);
coding->mode |= CODING_MODE_LAST_BLOCK;
}
@ -6116,7 +6119,7 @@ read_process_output (Lisp_Object proc, int channel)
/* Handling the process output should not deactivate the mark. */
Vdeactivate_mark = odeactivate;
unbind_to (count, Qnil);
SAFE_FREE_UNBIND_TO (count, Qnil);
return nbytes;
}
@ -8442,6 +8445,12 @@ returns non-`nil'. */);
doc: /* Name of external socket passed to Emacs, or nil if none. */);
Vinternal__daemon_sockname = Qnil;
DEFVAR_INT ("read-process-output-max", read_process_output_max,
doc: /* Maximum number of bytes to read from subprocess in a single chunk.
Enlarge the value only if the subprocess generates very large (megabytes)
amounts of data in one go. */);
read_process_output_max = 4096;
DEFSYM (Qinternal_default_interrupt_process,
"internal-default-interrupt-process");
DEFSYM (Qinterrupt_process_functions, "interrupt-process-functions");