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<B> Next:</B> <A NAME="tex2html1156" HREF="node64.html">semstat: A semtool companion </A>
<B>Up:</B> <A NAME="tex2html1154" HREF="node54.html">semtool: An interactive semaphore </A>
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<H4><A NAME="SECTION00743640000000000000">The Source</A></H4>
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<HR><PRE>/*****************************************************************************
Excerpt from &quot;Linux Programmer's Guide - Chapter 6&quot;
(C)opyright 1994-1995, Scott Burkett
*****************************************************************************
MODULE: semtool.c
*****************************************************************************
A command line tool for tinkering with SysV style Semaphore Sets
*****************************************************************************/
#include &lt;stdio.h&gt;
#include &lt;ctype.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;sys/types.h&gt;
#include &lt;sys/ipc.h&gt;
#include &lt;sys/sem.h&gt;
#define SEM_RESOURCE_MAX 1 /* Initial value of all semaphores */
void opensem(int *sid, key_t key);
void createsem(int *sid, key_t key, int members);
void locksem(int sid, int member);
void unlocksem(int sid, int member);
void removesem(int sid);
unsigned short get_member_count(int sid);
int getval(int sid, int member);
void dispval(int sid, int member);
void changemode(int sid, char *mode);
void usage(void);
int main(int argc, char *argv[])
{
key_t key;
int semset_id;
if(argc == 1)
usage();
/* Create unique key via call to ftok() */
key = ftok(&quot;.&quot;, 's');
switch(tolower(argv[1][0]))
{
case 'c': if(argc != 3)
usage();
createsem(&amp;semset_id, key, atoi(argv[2]));
break;
case 'l': if(argc != 3)
usage();
opensem(&amp;semset_id, key);
locksem(semset_id, atoi(argv[2]));
break;
case 'u': if(argc != 3)
usage();
opensem(&amp;semset_id, key);
unlocksem(semset_id, atoi(argv[2]));
break;
case 'd': opensem(&amp;semset_id, key);
removesem(semset_id);
break;
case 'm': opensem(&amp;semset_id, key);
changemode(semset_id, argv[2]);
break;
default: usage();
}
return(0);
}
void opensem(int *sid, key_t key)
{
/* Open the semaphore set - do not create! */
if((*sid = semget(key, 0, 0666)) == -1)
{
printf(&quot;Semaphore set does not exist!\n&quot;);
exit(1);
}
}
void createsem(int *sid, key_t key, int members)
{
int cntr;
union semun semopts;
if(members &gt; SEMMSL) {
printf(&quot;Sorry, max number of semaphores in a set is %d\n&quot;,
SEMMSL);
exit(1);
}
printf(&quot;Attempting to create new semaphore set with %d members\n&quot;,
members);
if((*sid = semget(key, members, IPC_CREAT|IPC_EXCL|0666))
== -1)
{
fprintf(stderr, &quot;Semaphore set already exists!\n&quot;);
exit(1);
}
semopts.val = SEM_RESOURCE_MAX;
/* Initialize all members (could be done with SETALL) */
for(cntr=0; cntr&lt;members; cntr++)
semctl(*sid, cntr, SETVAL, semopts);
}
void locksem(int sid, int member)
{
struct sembuf sem_lock={ 0, -1, IPC_NOWAIT};
if( member&lt;0 || member&gt;(get_member_count(sid)-1))
{
fprintf(stderr, &quot;semaphore member %d out of range\n&quot;, member);
return;
}
/* Attempt to lock the semaphore set */
if(!getval(sid, member))
{
fprintf(stderr, &quot;Semaphore resources exhausted (no lock)!\n&quot;);
exit(1);
}
sem_lock.sem_num = member;
if((semop(sid, &amp;sem_lock, 1)) == -1)
{
fprintf(stderr, &quot;Lock failed\n&quot;);
exit(1);
}
else
printf(&quot;Semaphore resources decremented by one (locked)\n&quot;);
dispval(sid, member);
}
void unlocksem(int sid, int member)
{
struct sembuf sem_unlock={ member, 1, IPC_NOWAIT};
int semval;
if( member&lt;0 || member&gt;(get_member_count(sid)-1))
{
fprintf(stderr, &quot;semaphore member %d out of range\n&quot;, member);
return;
}
/* Is the semaphore set locked? */
semval = getval(sid, member);
if(semval == SEM_RESOURCE_MAX) {
fprintf(stderr, &quot;Semaphore not locked!\n&quot;);
exit(1);
}
sem_unlock.sem_num = member;
/* Attempt to lock the semaphore set */
if((semop(sid, &amp;sem_unlock, 1)) == -1)
{
fprintf(stderr, &quot;Unlock failed\n&quot;);
exit(1);
}
else
printf(&quot;Semaphore resources incremented by one (unlocked)\n&quot;);
dispval(sid, member);
}
void removesem(int sid)
{
semctl(sid, 0, IPC_RMID, 0);
printf(&quot;Semaphore removed\n&quot;);
}
unsigned short get_member_count(int sid)
{
union semun semopts;
struct semid_ds mysemds;
semopts.buf = &amp;mysemds;
/* Return number of members in the semaphore set */
return(semopts.buf-&gt;sem_nsems);
}
int getval(int sid, int member)
{
int semval;
semval = semctl(sid, member, GETVAL, 0);
return(semval);
}
void changemode(int sid, char *mode)
{
int rc;
union semun semopts;
struct semid_ds mysemds;
/* Get current values for internal data structure */
semopts.buf = &amp;mysemds;
rc = semctl(sid, 0, IPC_STAT, semopts);
if (rc == -1) {
perror(&quot;semctl&quot;);
exit(1);
}
printf(&quot;Old permissions were %o\n&quot;, semopts.buf-&gt;sem_perm.mode);
/* Change the permissions on the semaphore */
sscanf(mode, &quot;%ho&quot;, &amp;semopts.buf-&gt;sem_perm.mode);
/* Update the internal data structure */
semctl(sid, 0, IPC_SET, semopts);
printf(&quot;Updated...\n&quot;);
}
void dispval(int sid, int member)
{
int semval;
semval = semctl(sid, member, GETVAL, 0);
printf(&quot;semval for member %d is %d\n&quot;, member, semval);
}
void usage(void)
{
fprintf(stderr, &quot;semtool - A utility for tinkering with semaphores\n&quot;);
fprintf(stderr, &quot;\nUSAGE: semtool4 (c)reate &lt;semcount&gt;\n&quot;);
fprintf(stderr, &quot; (l)ock &lt;sem #&gt;\n&quot;);
fprintf(stderr, &quot; (u)nlock &lt;sem #&gt;\n&quot;);
fprintf(stderr, &quot; (d)elete\n&quot;);
fprintf(stderr, &quot; (m)ode &lt;mode&gt;\n&quot;);
exit(1);
}</PRE>
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<I>Converted on: <BR>
Fri Mar 29 14:43:04 EST 1996</I>
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