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From: carolyn@cbmvax.UUCP (Carolyn Scheppner CATS)
Newsgroups: comp.sys.amiga
Subject: Re: Semaphores.
Message-ID: <2677@cbmvax.UUCP>
Date: Mon, 2-Nov-87 11:08:51 EST
Article-I.D.: cbmvax.2677
Posted: Mon Nov  2 11:08:51 1987
Date-Received: Fri, 6-Nov-87 03:29:03 EST
References: <8711012250.AA16257@cory.Berkeley.EDU>
Reply-To: carolyn@cbmvax.UUCP (Carolyn Scheppner CATS)
Organization: Commodore Technology, West Chester, PA
Lines: 191

In article <8711012250.AA16257@cory.Berkeley.EDU> dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:
>
>	Speaking of which, the documentation on the new Semaphore calls
>is seriously lacking.  It amounts to something like:
>
>	ObtainSemaphore(): This function obtains a semaphore.
>
>	Right... That really tells me how to use the function.  How about 
>some better docs on these functions??

   Here's an example.  Note that 1.2 Amiga.lib and Manx semaphore bindings
are bad.  This code contains workarounds.

----cut--here----
/** semaphore.c *************************************************************
*
*   Playing with public semaphores.
*
****************************************************************************/

#include <exec/types.h>
#include <exec/memory.h>
#include <exec/execbase.h>
#include <exec/semaphores.h>
#include <libraries/dos.h>

#ifdef AZTEC_C
#include <functions.h>
#endif

#include <stdio.h>

/* 
 * Use our versions of the semaphore functions
 */
#define RemSemaphore        myRemSemaphore  
#define FindSemaphore       myFindSemaphore 
#define AddSemaphore        myAddSemaphore


#define SSNAME	"mysemaphore"
#define SSSIZE  11

extern struct ExecBase *SysBase;

struct SignalSemaphore *FindSemaphore();

/* The bindings for "AddSemaphore" are broken in 1.2 Amiga.lib
 *
 * Dale's handcrafted AddSemaphore(). 
 */
VOID myAddSemaphore(ss)
struct SignalSemaphore *ss;
{
    InitSemaphore(ss);
    Forbid();
    Enqueue(&SysBase->SemaphoreList,ss);
    Permit();
}

#if AZTEC_C
VOID _cli_parse() {  }  /* save space, since we are not handling args */
#endif

main()
{
 struct SignalSemaphore *mysemaphore=0,*mysema=0;
 UBYTE	*ssname=0;
 
 mysema = (struct SignalSemaphore *) FindSemaphore(SSNAME);  
 if(mysema)
 {
    printf("Found semaphore: %s\n",mysema->ss_Link.ln_Name);
    RemSemaphore(mysema);
    *ssname='\0';
    FreeMem(mysema->ss_Link.ln_Name, (ULONG) SSSIZE+1);
    FreeMem(mysema, (ULONG) sizeof(*mysemaphore));
    exit(TRUE);
 }

 ssname = (UBYTE *) AllocMem( (ULONG) SSSIZE+1,MEMF_PUBLIC | MEMF_CLEAR); 
 if(!ssname)
 {
    printf("No space for name!\n");
    exit(TRUE);
 }
 	 
 mysemaphore = 
   (struct SignalSemaphore *) AllocMem( (ULONG) sizeof(*mysemaphore),MEMF_PUBLIC | MEMF_CLEAR);

 if(!mysemaphore)
 {
    FreeMem(ssname, (ULONG) SSSIZE+1);
    printf("No space for semaphore structure\n");
    exit(TRUE);
 }

 printf("Have memory...Now initializing and adding semaphore to system list.\n");

 strcpy(ssname,SSNAME);  
 mysemaphore->ss_Link.ln_Name = ( char * ) ssname;
 mysemaphore->ss_Link.ln_Pri  = 0;
 
 printf("AddSemaphore(%s)\n",mysemaphore->ss_Link.ln_Name); 

 AddSemaphore(mysemaphore);
 
 /* print name of semaphore */
 printf("FindSemaphore(%s)\n",mysemaphore->ss_Link.ln_Name); 

 mysema = (struct SignalSemaphore *) FindSemaphore(SSNAME);  
 if(!mysema)
  {
   printf("Not found semaphore: %s\n",ssname);
   *ssname='\0';
   FreeMem(ssname, (ULONG) SSSIZE+1);
   FreeMem(mysemaphore, (ULONG) sizeof(*mysemaphore));
   exit(TRUE);
  }

  printf("Found semaphore: %s\n",mysema->ss_Link.ln_Name);
  
  printf("ObtainSemaphore(%s)\n",mysemaphore->ss_Link.ln_Name); 
  
  ObtainSemaphore(mysema);  /* I won't come back until I have it... */

  printf("I have the semaphore: %s\n",mysema->ss_Link.ln_Name);
  
  printf("ReleaseSemaphore(%s)\n",mysemaphore->ss_Link.ln_Name); 

  ReleaseSemaphore(mysema);

  printf("RemSemaphore(%s)\n",mysemaphore->ss_Link.ln_Name);
   
  RemSemaphore(mysema);
  
  puts("Freeing memory used by semaphore.\n");

  *ssname='\0';
  FreeMem(ssname, (ULONG) SSSIZE+1);
  FreeMem(mysemaphore, (ULONG) sizeof(*mysemaphore));
  
  puts("All done.");
  	
}


/* The "C" interface code for the follow semaphore routines is broken in
 * Amiga.lib and in the Aztec C release 3.4a.
 *
 * @ Lattice people should cut and paste the assembler into a separate file.
 */
 
#if AZTEC_C     
#asm
; The exec.library function "AddSemaphore" is broken in KickStart rel. 33.180
;
        
        XREF    _SysBase
        XREF    _LVOFindSemaphore
;	XREF    _LVOAddSemaphore
	XREF    _LVORemSemaphore


	XDEF    _myFindSemaphore
;       XDEF    _myAddSemaphore
	XDEF    _myRemSemaphore

_myFindSemaphore:
	move.l 	4(sp),a1
        move.l 	_SysBase,a6
	jmp 	_LVOFindSemaphore(a6)
;
;_myAddSemaphore:
;	move.l 	4(sp),a1
;       move.l 	_SysBase,a6
;	jmp 	_LVOAddSemaphore(a6)

_myRemSemaphore:
	move.l 	4(sp),a1
        move.l 	_SysBase,a6
	jmp 	_LVORemSemaphore(a6)
#endasm
#endif

-- 
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Carolyn Scheppner -- CATS   >>Commodore Amiga Technical Support<<
                     UUCP  ...{allegra,ihnp4,rutgers}!cbmvax!carolyn 
                     PHONE 215-431-9180
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