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From: bob <bob AT icanprogram DOT com>
To: cygwin AT cygwin DOT com
Subject: Fifo blocking and performance issues - some test code snips
Date: Wed, 03 Oct 2012 11:44:24 -0400
Message-ID: <122663406.srZGqP3Ccr@bob-kubuntu>
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I'm on the mailing list in digest mode,   so this response may not get 
threaded correctly.

Here is some basic test code which illustrates all the things I spoke about in 
my previous note.   The Cygwin machine and the Linux machine are identical (I 
have a harddrive swap system).    Notice that the Cygwin is 2 orders of 
magnitude slower.   Also notice the "Resource temporarily unavailable" error 
occurring throughout the Cygwin output but never in the Linux output.

Thanks again in advance for all your help on this problem.

bob

=========== begin sender.c ===========
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <time.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/select.h>
#include <sys/timeb.h>

int blocked_read(int, char *, int);

int main(int argc, char *argv[])
{
char command[80];
char fifoname[80];
int fd=-1;
int rfd;
int i;
int j;
int *r;
int bytesToGo;
int numBytes;
char buf[5];
char *p;
int rc;
struct timeb before;
struct timeb after;
int msec;

printf("fifo sender starting\n");

sprintf(fifoname,"/tmp/fsender");

mkfifo(fifoname, 0666);
chmod(fifoname, 0666);

printf("starting receiver\n");

sprintf(command,"./receiver&");
rc=system(command); 

printf("receiver started\n");

sleep(2);

fd=open(fifoname, O_RDWR|O_NONBLOCK);
//fd=open(fifoname, O_RDONLY|O_NONBLOCK);
rfd=open("/tmp/freceiver", O_WRONLY);

ftime(&before);

for(j=1; j<100; j++)
	{
printf("j=%d\n",j);

	write(rfd,&j,sizeof(int));

	numBytes=0;
	memset(buf,0,4);
	p=buf;
	for(i=0; i< 10; i++)
		{
		bytesToGo=sizeof(int) - numBytes;

printf("bytesToGo=%d numBytes=%d\n",bytesToGo,numBytes);

		if(bytesToGo <= 0) break;

		rc=blocked_read(fd,p,bytesToGo);
printf("sender rc[%d]=%d\n",i,rc);
		if(rc == 0)
			{
			printf("got eof\n");
//		close(fd);
//		fd=open(fifoname, O_RDONLY);
			}
		else
		if(rc == -1)
			{
			printf("%s\n",strerror(errno));
			}
		else
			{
			numBytes+=rc;
			p+=rc;
			}
		} //end for i

printf("buf: 0x%X-%X-%X-%X\n",buf[0],buf[1],buf[2],buf[3]);
	r=(int *)buf;

printf("reply[%d]=%d\n",j,*r);
	} // end for j

ftime(&after);
msec=(after.time - before.time)*1000 + (after.millitm - before.millitm);
printf("%d messages took %d ms\n",j, msec);

sleep(1);

unlink(fifoname);
unlink("/tmp/freceiver");
	
exit(0);
} // end sender


int blocked_read(int fd, char *buff, int size)
{
int rc;
fd_set inset;

FD_ZERO(&inset);
FD_SET(fd, &inset);

printf("send: before select\n");
select(fd+1, &inset, NULL, NULL, NULL);
printf("send: before read\n");
rc=read(fd,buff,size);

printf("send: read rc=%d\n",rc);
return(rc);
} // end blocked_read
=========== end sender.c =============

=========== begin receiver.c =========

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/select.h>

int blocked_read(int, char *, int);

int main(int argc, char *argv[])
{
char command[80];
char fifoname[80];
int fd;
int rfd;
int dummy;
int i;
int j;
int k;
int *r;
int bytesToGo;
int numBytes;
char buf[4];
char *p;
int rc;

printf("fifo receiver starting\n");

sprintf(fifoname,"/tmp/freceiver");

mkfifo(fifoname, 0666);
chmod(fifoname, 0666);

fd=open(fifoname, O_RDWR | O_NONBLOCK);
//fd=open(fifoname, O_RDONLY | O_NONBLOCK);

for(k=0; k<99; k++)
	{
	numBytes=0;
	p=buf;
	for(i=0; i< 10; i++)
		{
		bytesToGo=sizeof(int) - numBytes;

		if(bytesToGo <= 0) break;

//	rc=read(fd,p,bytesToGo);
		rc=blocked_read(fd,p,bytesToGo);
printf("recv rc[%d]=%d\n",i,rc);
		if(rc == 0)
			{
			printf("recv eof\n");
			}
		else
		if(rc == -1)
			{
			printf("%s\n",strerror(errno));
			}
		else
			{
			numBytes+=rc;
			p+=rc;
			}
		} // end for i

	r=(int *)buf;
	j=*r;
printf("received[%d]=%d\n",k,j);
	j++;

//	sleep(1);
	
	rfd=open("/tmp/fsender", O_WRONLY);
	write(rfd,&j,sizeof(int));
	close(rfd);
	} // end for k

unlink(fifoname);

exit(0);
} // end receiver

int blocked_read(int fd, char *buff, int size)
{
int rc;
fd_set inset;

FD_ZERO(&inset);
FD_SET(fd, &inset);

printf("recv: before select\n");
select(fd+1, &inset, NULL, NULL, NULL);
printf("recv: before read\n");
rc=read(fd,buff,size);

printf("recv: read rc=%d\n",rc);

return(rc);
} // end blocked_read
=========== end receiver.c ===========

=========== begin linux.out ==========
sender
fifo sender starting
starting receiver
receiver started
fifo receiver starting
recv: before select
j=1
bytesToGo=4 numBytes=0
send: before select
recv: before read
recv: read rc=4
recv rc[0]=4
received[0]=1
recv: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x2-0-0-0
reply[1]=2
j=2
bytesToGo=4 numBytes=0
send: before select
recv: before read
recv: read rc=4
recv rc[0]=4
received[1]=2
recv: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x3-0-0-0
reply[2]=3
j=3
bytesToGo=4 numBytes=0
send: before select
recv: before read
recv: read rc=4
recv rc[0]=4
received[2]=3
recv: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x4-0-0-0
reply[3]=4

...

j=94
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[93]=94
recv: before select
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x5F-0-0-0
reply[94]=95
j=95
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[94]=95
recv: before select
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x60-0-0-0
reply[95]=96
j=96
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[95]=96
recv: before select
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x61-0-0-0
reply[96]=97
j=97
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[96]=97
recv: before select
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x62-0-0-0
reply[97]=98
j=98
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[97]=98
recv: before select
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x63-0-0-0
reply[98]=99
j=99
bytesToGo=4 numBytes=0
recv: before read
recv: read rc=4
recv rc[0]=4
received[98]=99
send: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x64-0-0-0
reply[99]=100
100 messages took 12 ms
=========== end linux.out ============

=========== begin cygwin.out =========
$ sender
fifo sender starting
starting receiver
receiver started
fifo receiver starting
recv: before select
j=1
bytesToGo=4 numBytes=0
send: before select
recv: before read
recv: read rc=4
recv rc[0]=4
received[0]=1
recv: before select
send: before read
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x2-0-0-0
reply[1]=2
j=2
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[1]=2
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x3-0-0-0
reply[2]=3
j=3
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[2]=3
send: read rc=-1
sender rc[0]=-1
Resource temporarily unavailable
bytesToGo=4 numBytes=0
send: before select
recv: before select
send: before read
send: read rc=4
sender rc[1]=4
bytesToGo=0 numBytes=4
buf: 0x4-0-0-0
reply[3]=4
j=4
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[3]=4
send: read rc=-1
sender rc[0]=-1
Resource temporarily unavailable
bytesToGo=4 numBytes=0
send: before select
recv: before select
send: before read
send: read rc=4
sender rc[1]=4
bytesToGo=0 numBytes=4
buf: 0x5-0-0-0
reply[4]=5
j=5
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[4]=5
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x6-0-0-0
reply[5]=6
j=6
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[5]=6
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x7-0-0-0
reply[6]=7

...

j=90
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[89]=90
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x5B-0-0-0
reply[90]=91
j=91
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[90]=91
send: read rc=-1
sender rc[0]=-1
Resource temporarily unavailable
bytesToGo=4 numBytes=0
send: before select
recv: before select
send: before read
send: read rc=4
sender rc[1]=4
bytesToGo=0 numBytes=4
buf: 0x5C-0-0-0
reply[91]=92
j=92
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[91]=92
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x5D-0-0-0
reply[92]=93
j=93
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[92]=93
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x5E-0-0-0
reply[93]=94
j=94
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[93]=94
send: read rc=-1
sender rc[0]=-1
Resource temporarily unavailable
bytesToGo=4 numBytes=0
send: before select
recv: before select
send: before read
send: read rc=4
sender rc[1]=4
bytesToGo=0 numBytes=4
buf: 0x5F-0-0-0
reply[94]=95
j=95
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[94]=95
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x60-0-0-0
reply[95]=96
j=96
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[95]=96
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x61-0-0-0
reply[96]=97
j=97
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[96]=97
send: read rc=-1
sender rc[0]=-1
Resource temporarily unavailable
bytesToGo=4 numBytes=0
send: before select
recv: before select
send: before read
send: read rc=4
sender rc[1]=4
bytesToGo=0 numBytes=4
buf: 0x62-0-0-0
reply[97]=98
j=98
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[97]=98
recv: before select
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x63-0-0-0
reply[98]=99
j=99
bytesToGo=4 numBytes=0
send: before select
send: before read
recv: before read
recv: read rc=4
recv rc[0]=4
received[98]=99
send: read rc=4
sender rc[0]=4
bytesToGo=0 numBytes=4
buf: 0x64-0-0-0
reply[99]=100
100 messages took 967 ms
done
=========== end cygwin.out ===========


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