/*
	sharedmem.c

	Started by Jeff Ondich on 4/11/96
	Last modified on 4/3/02

	This program demonstrates how to use shared memory
	in Linux.
*/

#include	<sys/types.h>
#include	<sys/wait.h>
#include	<sys/ipc.h>
#include	<sys/shm.h>
#include	<unistd.h>
#include	<stdlib.h>
#include	<string.h>
#include	<stdio.h>


#define		kSharedMemKey		((key_t)1113)
#define		kSharedBufferSize	100


int main( void )
{
	int			pid, status;
	char		*pSharedBuffer;
	int			sharedBufferID;


	/* Create the shared memory. */

	sharedBufferID = shmget( kSharedMemKey,
							 kSharedBufferSize,
							 0664 | IPC_CREAT | IPC_EXCL  );

	if( sharedBufferID == -1 )
	{
		perror( "Shmget trouble" );
		exit( 1 );
	}


	/* Attach the shared memory to the current process' address space. */

	pSharedBuffer = (char *)shmat( sharedBufferID, (char *)0, 0 );
	if( pSharedBuffer == (char *)-1 )
	{
		perror( "Shmat trouble" );
		shmctl( sharedBufferID, IPC_RMID, NULL );
		exit( 1 );
	}


	/* Initialize the shared memory. */

	strcpy( pSharedBuffer, "Mom, there's a singing moose outside!\n" );
	printf( "%s", pSharedBuffer );


	/* Fork a child process */

	pid = fork();
	if( pid == -1 )
	{
		perror( "fork() failure" );
	}

	else if( pid != 0 )
	{
		printf( "The parent %d is waiting.\n", getpid() );
		wait( &status );
		printf( "The state of affairs is: %s\n", pSharedBuffer );
	}

	else
	{
		printf( "The child %d is ready to shoo the moose away.\n", getpid() );
		strcpy( pSharedBuffer, "The moose is gone now." );
	}

	printf( "%d is quitting\n", getpid() );
	fflush( stdout );


	/* Clean up the shared memory. */

	shmctl( sharedBufferID, IPC_RMID, NULL );
	shmdt( pSharedBuffer );

	return( 0 );
}