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Experiment about select() versus non-blocking i/o. select() lost.

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This commit is contained in:
Thomas Schmitt 2009-04-05 14:48:03 +02:00
parent f2b7872fc6
commit b27bcc7022
1 changed files with 73 additions and 1 deletions
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74
libisofs/filters/external.c
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@ -17,6 +17,7 @@
#include "../fsource.h"
#include <sys/types.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>
#include <signal.h>
@ -25,6 +26,9 @@
#include <errno.h>
#include <string.h>
#ifdef Libisofs_external_filters_selecT
#include <sys/select.h>
#endif
/*
* A filter that starts an external process and uses its stdin and stdout
@ -230,8 +234,8 @@ int extf_stream_open_flag(IsoStream *stream, int flag)
/* <<< TEST <<<
*/
ret= ISO_FILE_READ_ERROR;
*/
if (ret < 0) {
/* Dispose pipes and child */
@ -322,6 +326,59 @@ int extf_stream_open(IsoStream *stream)
}
#ifdef Libisofs_external_filters_selecT
/* Performance is weaker than with non-blocking i/o and usleep(). */
static
int extf_wait_for_io(int fd_in, int fd_out, int microsec, int flag)
{
struct timeval wt;
fd_set rds,wts,exs;
int ready, fd_max;
fd_max = fd_out;
if (fd_in > fd_out)
fd_max = fd_in;
FD_ZERO(&rds);
FD_ZERO(&wts);
FD_ZERO(&exs);
if (fd_in >= 0) {
FD_SET(fd_in,&rds);
FD_SET(fd_in,&exs);
}
if (fd_out >= 0) {
FD_SET(fd_out,&rds);
FD_SET(fd_in,&exs);
}
wt.tv_sec = microsec/1000000;
wt.tv_usec = microsec%1000000;
ready = select(fd_max + 1, &rds, &wts, &exs, &wt);
if (ready <= 0)
return 0;
if (fd_in >= 0) {
if (FD_ISSET(fd_in, &rds))
return 1;
}
if (fd_out >= 0) {
if (FD_ISSET(fd_out, &rds))
return 2;
}
if (fd_in >= 0) {
if (FD_ISSET(fd_in, &exs))
return -1;
}
if (fd_out >= 0) {
if (FD_ISSET(fd_out, &exs))
return -2;
}
return(0);
}
#endif /* Libisofs_external_filters_selecT */
static
int extf_stream_read(IsoStream *stream, void *buf, size_t desired)
{
@ -417,10 +474,25 @@ int extf_stream_read(IsoStream *stream, void *buf, size_t desired)
if (ret == -1) {
if (errno == EAGAIN) {
#ifdef Libisofs_external_filters_selecT
/* >>> ??? should one replace non-blocking read()
by select () ? */
/* This saves 10 % CPU load but needs 50 % more real time*/
ret = extf_wait_for_io(running->recv_fd, running->send_fd,
100000, 0);
if (ret < 0)
usleep(1000); /* To make sure sufficient laziness */
#else
/* No sleeping needs 90 % more CPU and saves 6 % time */
usleep(1000); /* go lazy because the filter is slow */
#endif /* NIX */
continue;
}