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Top Forums Programming pipe() and poll() problem in C Post 302478629 by blackmamba21 on Wednesday 8th of December 2010 12:49:48 PM
Old 12-08-2010
pipe() and poll() problem in C

Hi all,
Im trying to do a simple program which ask the user for a unix command with the arguments. The program fork and the two process communicate with pipes. The child process call execvp with the command and the father process read the result of the execvp via the pipe.

This program works well with basic commands like ls or echo but when there's interaction between the user and the process for example tr a-z A-Z I think i get a broken pipe on the writing end of my pipe from the parent to the child.

In the parent process, I also have to poll between what the user type and what the child process send but I don't think this is the problem.

here's my code, the name variable and error messages are in french but you get the idea. thank u very much and sorry for bad english.

If you have any questions feel free to ask

Code:
void executerCommande( char *commande[], int descripteur, char* option )
{
	int tubeEntree[2];
	int tubeSortie[2];
	int erreur;
	
	erreur = pipe( tubeEntree );
	if ( erreur == -1 )
	{
		printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
		exit( 1 );
	}
	erreur = pipe( tubeSortie );
	if ( erreur == -1 )
	{
		printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
		exit( 1 );
	}

	pid_t pid = fork();
	if ( pid == -1 )	// erreur
	{
		perror( "fork a échoué" );
		exit( 1 );
	}
	else if ( pid == 0 )	// child
	{
		close( tubeEntree[1] );		// closing writing end of tube from parent to child
		close( tubeSortie[0] );		// closing reading end of tube from child to parent

		dup2( tubeSortie[1], STDOUT_FILENO );	// redirecting stdout to writing end of tube from child to parent
		close( tubeSortie[1] );		// fermeture du doublon

		dup2( tubeEntree[0], STDIN_FILENO );	// redirecting stdin to reading end of tube from parent to child
		close( tubeEntree[0] );		// fermeture du doublon
		execvp( commande[0], commande );
	}
	else		// parent
	{
		int evenement;
		int commandeTerminee = 0;
		char tampon [256];
		struct pollfd entrees[2];
		entrees[0].fd = 0;		// check stdin
		entrees[0].events = POLLIN | POLLPRI;		// surveiller pour des données normales ou prioritaires
		entrees[0].revents = 0;
		entrees[1].fd = tubeSortie[0];		// check reading end of tube from child to parent
		entrees[1].events = POLLIN | POLLPRI;		// surveiller pour des données normales ou prioritaires
		entrees[1].revents = 0;

		close( tubeEntree[0] );		// closing reading end of tube from parent to child
		close( tubeSortie[1] );		// closing writing end of tube from child to parent
		
		while ( commandeTerminee == 0 )
		{
			evenement = poll( entrees, 2, 0 );
			if ( evenement == -1 )
			{
				printf( "Erreur lors du poll %s\n", strerror( errno ) );
				exit( 1 );
			}
			if ( ( entrees[0].revents & POLLIN ) || ( entrees[0].revents & POLLPRI ) )
			{
				memset(tampon, '\0', 256);
				read( entrees[0].fd, tampon, 256 );
				if ( ( strcmp( option, "-i" ) == 0 ) || ( strcmp( option, "-io" ) == 0 ) )
				{
					erreur = write ( descripteur, tampon, strlen( tampon ) );
					if ( erreur == -1 )
					{
						printf( "Erreur lors de l'écriture sur le fichier %s\n", strerror( errno ) );
						exit( 1 );
					}
				}
				erreur = write ( tubeEntree[1], tampon, strlen( tampon ) );
				printf( "Ecriture enfant\n" );
				if ( erreur == -1 )
				{
					printf( "Erreur lors de l'écriture dans le tube d'entrée %s\n", strerror( errno ) );
					exit( 1 );
				}
			entrees[0].revents = 0;
			}
			if ( ( entrees[1].revents & POLLIN ) || ( entrees[1].revents & POLLPRI ) )
			{
				do {
					memset(tampon, '\0', 256);
					erreur = read( entrees[1].fd, tampon, 256 );
					if ( erreur == -1 )	
					{
						printf( "Erreur lors de la lecture du tube de sortie %s\n", strerror ( errno ) );
						exit( 1 );
					}
					if ( ( strcmp( option, "-o" ) == 0 ) || ( strcmp( option, "-io" ) == 0 ) )
					{
						erreur = write( descripteur, tampon, strlen( tampon ) );
						if ( erreur == -1 )	
						{
							printf( "Erreur lors de l'écriture sur le fichier %s\n", strerror ( errno ) );
							exit( 1 );
						}
					}
					printf( "%s", tampon );
				} while (erreur != 0);
			entrees[1].revents = 0;
			}
			if ( entrees[1].revents & POLLHUP )
			{
				commandeTerminee = 1;
			}
		}	
		pid = wait( NULL );
	}
}

---------- Post updated at 12:49 PM ---------- Previous update was at 11:26 AM ----------

I have force a read in the pipe connecting the child process ( the command ) to my parent process and there's nothing so my problem is either 1) the information coming from the user is not arriving at the child or the child is not writing properly in the exit pipe.

Any help would be appreciated... Its my first time with pipes
 

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