PoC: /* Blocking Calls */ Completing the sentence

2022-08-13T14:34:45Z

Blocking Calls: Completing the sentence

← Older revision		Revision as of 16:34, 13 August 2022
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	If the application program is "stuck" in kind of a wait condition, it depends on the wait condition if the blocking call is cancelled, allowing the application code to take control again.		If the application program is "stuck" in kind of a wait condition, it depends on the wait condition if the blocking call is cancelled, allowing the application code to take control again.

	This code snippet shows an example how to restart		This code snippet shows an example how to restart an interrupted recv() from a socket by restarting the <code>while</code> loop.

	/* Main loop. */		/* Main loop. */
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	}		}

	Some OS' automatically restart the last operation if it became interrupted by a signal. OS/400 V4R5 does not, so we restart in a loop, making this example a generic restart function, if <code>EINTR</code> is given as error reason.		<blockquote>'''Note''': Some OS' automatically restart the last operation if it became interrupted by a signal. OS/400 V4R5 does not, so we restart in a loop, making this example a generic restart function, if <code>EINTR</code> is given as error reason.

	[[Category: Programming]]		[[Category: Programming]]

PoC: New

2022-08-13T14:23:05Z

New

New page

'''Properly ending a daemon''', or background task can be done in multiple ways. Since we're using C as programming language, using the UNIX way of handling this affair proved to be most easy.

OS/400 incorporates quite a bit of UNIX APIs, including signals. If you use option 4 on <code>wrkactjob</code>, or end the subsystem the job in question is running within, SIGTERM is being sent to tell the application program to cleanly end.

== Using the signal API ==
In short, declare the necessary infrastructure for a signal, and make it do something.

#include <string.h>
#include <signal.h>
#include <stdlib.h>

/* Using this globally eases handling. */
int exit_flag = 0;

void set_exit_flag(int signum) {
/* We ignore signum, because we only watch for SIGTERM. */
exit_flag = 1;
}

int main() {
struct sigaction termaction;

/* Create signal handler for SIGTERM. */
memset(&termaction, 0, sizeof(struct sigaction));
termaction.sa_handler = set_exit_flag;
sigaction(SIGTERM, &termaction, NULL);

/* Main loop. */
while( exit_flag == 0 ) {
...
}

/* Add cleanup routines here. */

exit(0);
}

In our case, we set <code>exit_flag</code> to 1, so the program exits from its main loop at the next iteration.

=== Blocking Calls ===
If the application program is "stuck" in kind of a wait condition, it depends on the wait condition if the blocking call is cancelled, allowing the application code to take control again.

This code snippet shows an example how to restart

/* Main loop. */
while( exit_flag == 0 ) {

/* Handle incoming network data. */
if ( (n = recv(sockfd, rcvBuf, BUFSIZE, 0)) == -1) {
if ( errno == EINTR ) {
continue;
} else {
/* Some other error happened. Handle next request. */
Qp0zLprintf("recv(): %s\n", strerror(errno));
break;
}
}

/* Do things with the received data. */
}

Some OS' automatically restart the last operation if it became interrupted by a signal. OS/400 V4R5 does not, so we restart in a loop, making this example a generic restart function, if <code>EINTR</code> is given as error reason.

[[Category: Programming]]

Properly ending a daemon written in C - Revision history

PoC: /* Blocking Calls */ Completing the sentence

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