cygserver - Postgres Multiple connection Load Testing - Inifinte Loop

[Marco Atzeri]

On 24/03/2017 18:11, Corinna Vinschen wrote:
> Hi Noah,
>

>>
>> On GNU/Linux, AIX, and Solaris, the processes keep busy and finish one million
>> lock/unlock cycles apiece in a few minutes.  On Cygwin, they hang within a few
>> seconds and under one hundred cycles apiece.  At that point, cygserver is
>> unresponsive to other clients; for example, "strace /bin/true", opening a new
>> Cygwin terminal, "cat /proc/sysvipc/sem" and "cygserver -S" all hang.  In most
>> tests, cygserver was not consuming CPU while unresponsive.
>
>
> I pushed a patchset now, and uploaded new developer snapshots for
> testing to https://cygwin.com/snapshots/
>
> I'm also going to create a 2.8.0-0.4 test release later today.
>
> Please give it a try, and please note that *all* patches affect
> cygserver itself, so you have to test the new cygserver in the
> first place.  The Cygwin DLL is not affected by the changes.
>
>
> Thanks,
> Corinna
>

Hi Corinna,
just noted a small glitch.

Attached a modification of Noah's test, it now accepts the number of 
workers and semaphore are as before workers/4

./sema_parallel-2 32
  worker ....
  OK

./sema_parallel-2 64
semget
semget: Invalid argument

If I restart the cygserver

./sema_parallel-2 64
  worker ....
  OK

./sema_parallel-2 128
semget
semget: Invalid argument


It seems that the number of max available semaphores is frozen to first 
call value.









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/*
 * Demonstrate cygserver hang under concurrent sysv semaphore traffic.  Run
 * without arguments.  Output will cease within a few seconds, and cygserver
 * will be unresponsive to all clients.
 *
 * This is compatible with default cygserver settings; it uses a single
 * semaphore set of four semaphores.
 */

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#define SEM_KEY 0x631a2c3e
#define N_CYCLE 1000000

union semun
{
    int val;
    struct semid_ds *buf;
    unsigned short *array;
};

static int print_every = 1;


/* In parallel, N_WORKER processes run this function. */
static int do_worker(int ordinal, int set, int N_SEMA)
{
    int i;
    struct sembuf op;

    printf("start worker %d\n", ordinal);
    fflush(stdout);

    op.sem_flg = 0;
    for (i = 1; i <= N_CYCLE; i++)
    {
	op.sem_num = random() % N_SEMA;

	op.sem_op = -1;
	if (0 > semop(set, &op, 1))
	{
	    perror("semop");
	    return 1;
	}

	op.sem_op = 1;
	if (0 > semop(set, &op, 1))
	{
	    perror("semop");
	    return 1;
	}

	if (i % print_every == 0)
	{
	    printf("worker %d: %d cycles elapsed\n", ordinal, i);
	    fflush(stdout);
	}
    }

    return 0;
}

int main(int argc, char **argv)
{
    int status = 1, set, i, child_status;

    int N_WORKER,  N_SEMA;

    switch(argc){
        case 3:
	    print_every = atoi(argv[2]);
        case 2:
             N_WORKER=atoi(argv[1]);
             N_SEMA= (N_WORKER/4);
	     break;
        default:
	     fprintf(stderr, "Usage: sema_parallel workers [print-every-N]\n");
	     return status;
    }

    puts("semget");
    fflush(stdout);
    set = semget(SEM_KEY, N_SEMA, IPC_CREAT | 0600);
    if (set == -1)
    {
	perror("semget");
	return status;
    }

    puts("SETVAL");
    fflush(stdout);
    for (i = 0; i < N_SEMA; i++)
    {
	union semun s;
	s.val = 1;

	if (0 > semctl(set, i, SETVAL, s))
	{
	    perror("semctl(SETVAL)");
	    goto cleanup;
	}
    }

    for (i = 0; i < N_WORKER; i++)
    {
	pid_t pid;
	pid = fork();
	switch (pid)
	{
	    case -1:
		perror("fork");
		goto cleanup;
	    case 0:
		return do_worker(i, set, N_SEMA );
	}
    }

    status = 0;

cleanup:
    while (wait(&child_status) != -1)
	;
    if (errno != ECHILD)
    {
	perror("wait");
	status = 1;
    }

    if (0 > semctl(set, 0, IPC_RMID))
    {
	perror("semtctl(IPC_RMID)");
	status = 1;
    }

    return status;
}

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