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From: jimg@hp-ptp.HP.COM (Jim_Garrison)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Amiga semaphores (HELP!)
Message-ID: <2290009@hp-ptp.HP.COM>
Date: 27 Sep 90 14:47:05 GMT
References: <2290004@hp-ptp.HP.COM>
Organization: HP Pacific Technology Park - Sunnyvale, Ca.
Lines: 93


Yahoo, thanks to Peter Xrbfk, I now have working Amiga semaphores.  I guess 
that my problem was that FindSemaphore() doesn't work either.  I have included
Peter's example program which works fine for me.  As someone else mentioned,
I think it might be a good idea to include this information in the Amiga 
introduction.

Thank you all for your help,

Jim Garrison
Hewlett Packard
jimg@hpiatmh
(408) 746-5349


>Hi, Jim.
>
>I suppose it was I who tried to post this to you at the wrong address.
>
>This works on my A500, ie. creates the semaphore once, and finds it 
>afterwards. It did not work with FindSemaphore() which seems to have
>a slight hitch in that it expects the name in A1 and not in A0 as indicated
>in the .fd file. One could consider this to be an error of the compiler
>makers who have not noticed this.
>
>With Aztec C 3.4 this program does the trick, but it shouldn't
>be compiler dependent.
>
>I hope this works for you too.
>
>
>  - Peter (poe@daimi.aau.dk)
>
---- cut here ----
/* sem.c */

/*
   Created 26-Sep-90 by Peter Xrbfk.
   This works on my A500 (KS 33.180 / WB 34.20)
*/

#include	"exec/types.h"
#include	"exec/semaphores.h"
#include	"exec/execbase.h"
#include	"exec/memory.h"
#include	"stdio.h"


struct Node *FindName();
void *AllocMem();
char *strcpy();

extern struct ExecBase *SysBase;

/*
   Define private version of FindSemaphore() because FindSemaphore()
   really expects the namepointer in A1 and not in A0 as indicated
   in the .fd files
*/

#define FindSem(s) (struct SignalSemaphore *)FindName(&SysBase->SemaphoreList,s)

main()
{
	struct SignalSemaphore *ss;
	char *str;

	if(!(ss = FindSem("MySem"))) {
		printf("didn't find semaphore\n");
		ss = (struct SignalSemaphore *)
			AllocMem((long)sizeof(struct SignalSemaphore),
				 MEMF_PUBLIC|MEMF_CLEAR);
		/* assume ok */
		InitSemaphore(ss);
		str = AllocMem(10L,MEMF_PUBLIC);
		ss->ss_Link.ln_Name = strcpy(str,"MySem");
		ss->ss_Link.ln_Pri = 0;

		printf("adding it\n");
		/* add it */
		Forbid();
		AddTail(&SysBase->SemaphoreList,ss);
		Permit();
		printf("semaphore created and added\n");
	}

	/* use it for something */
	ObtainSemaphore(ss);

	printf("bla\n");

	ReleaseSemaphore(ss);
}