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/* libguestfs
* Copyright (C) 2013 Red Hat Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <error.h>
#include <errno.h>
#include <libintl.h>
#include "guestfs.h"
#include "guestfs-utils.h"
#include "estimate-max-threads.h"
static char *read_line_from (const char *cmd);
/* The actual overhead is likely much smaller than this, but err on
* the safe side.
*/
#define MBYTES_PER_THREAD 650
/**
* This function uses the output of C<free -m> to estimate how many
* libguestfs appliances could be safely started in parallel. Note
* that it always returns E<ge> 1.
*/
size_t
estimate_max_threads (void)
{
CLEANUP_FREE char *mbytes_str = NULL;
size_t mbytes;
/* Choose the number of threads based on the amount of free memory. */
mbytes_str = read_line_from ("LANG=C free -m | "
"grep '^Mem' | awk '{print $4+$6+$7}'");
if (mbytes_str == NULL)
return 1;
if (sscanf (mbytes_str, "%zu", &mbytes) != 1)
return 1;
return MAX (1, mbytes / MBYTES_PER_THREAD);
}
/**
* Run external command and read the first line of output.
*/
static char *
read_line_from (const char *cmd)
{
FILE *pp;
char *ret = NULL;
size_t allocsize = 0;
pp = popen (cmd, "r");
if (pp == NULL)
error (EXIT_FAILURE, errno, "%s: external command failed", cmd);
if (getline (&ret, &allocsize, pp) == -1)
error (EXIT_FAILURE, errno, "could not read line from external command");
if (pclose (pp) == -1)
error (EXIT_FAILURE, errno, "pclose");
return ret;
}
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