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From "Brad Nicholes" <BNICHO...@novell.com>
Subject RE: cvs commit: apr/atomic/netware apr_atomic.c
Date Thu, 28 Mar 2002 17:05:07 GMT
I understand.  How are the other platforms handling this issue then if
they define APR_ATOMIC_NEED_DEFAULT = 0 and APR_ATOMIC_NEED_CAS_DEFAULT
= 1?  If they do this then some of the atomic operations are defined as
macros to the native OS functions and the _cas operations are
implemented as apr_ functions.  Isn't this the same situations that
NetWare is currently doing and is incorrect?  It seems that the atomic
functions should be all or nothing.  Either the OS implements them all
through native functions or it takes the default implementation.

Brad

Brad Nicholes
Senior Software Engineer
Novell, Inc., a leading provider of Net business solutions
http://www.novell.com 

>>> Ian Holsman <Ian.Holsman@cnet.com> Thursday, March 28, 2002 9:20:59
AM >>>
 
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> -----Original Message-----
> From: Brad Nicholes [mailto:BNICHOLES@novell.com] 
> Sent: Thursday, March 28, 2002 7:27 AM
> To: apr-cvs@apache.org; dev@apr.apache.org; Ian.Holsman@cnet.com 
> Subject: RE: cvs commit: apr/atomic/netware apr_atomic.c
> 
> 
> Thanks for the catch on the _inc instead of _dec.  I copied and
> pasted the wrong function.  Actually the only reason why I had to
> implement apr_atomic_dec was because of the return value.  The
> NetWare
> implementation returns a void where apr_atomic_dec returns an int. 

same as FreeBSD.. which make it useless for reference counting IMHO

> Since atomic_dec() is a NetWare native function there should be no
> problem with a race condition.  The locking is all handled by the
> OS.  
thats not where the race occurs.
you've gone and decremented it in  atomic way with your system call.
you then get swapped out something goes and does something to the
variable
(say increment it)
you then get swapped back in.
and return *mem.
but you've lost the decrement.

> As far as the _cas goes, this was taken straight from the Unix
> implementation.  If it is wrong for NetWare then it is probably
> wrong for Unix also.

the unix implementation works as it locks ALL access to the variable
with a mutex the problem is you've only locked the un-implemennted
versions

> 
> Brad
> 
> Brad Nicholes
> Senior Software Engineer
> Novell, Inc., a leading provider of Net business solutions
> http://www.novell.com 
> 
> >>> Ian.Holsman@cnet.com Wednesday, March 27, 2002 5:46:37 PM >>> 
>  
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> 
> hi.
> 
> this wont work as you still have race conditions
> in the 2 functions you implented (the _dec and _cas)
> oh.. and the _dec looks like it is adding instead of subtracting
> 
> is novell x86 only ?
> I'm thinking of just grabbing freeBSD's atomic implementation
> and using that as the default x86 implementation.
> 
> > -----Original Message-----
> > From: bnicholes@apache.org [mailto:bnicholes@apache.org] 
> > Sent: Wednesday, March 27, 2002 3:52 PM
> > To: apr-cvs@apache.org 
> > Subject: cvs commit: apr/atomic/netware apr_atomic.c
> > 
> > 
> > bnicholes    02/03/27 15:51:51
> > 
> >   Modified:    .        NWGNUmakefile
> >                build    nw_export.inc
> >                include  apr_atomic.h
> >   Added:       atomic/netware apr_atomic.c
> >   Log:
> >   Added the NetWare version of atomic.c to the build
> >   
> >   Revision  Changes    Path
> >   1.2       +5 -0      apr/NWGNUmakefile
> >   
> >   Index: NWGNUmakefile
> >  
> > ==================================================================
> > = 
> >   RCS file: /home/cvs/apr/NWGNUmakefile,v
> >   retrieving revision 1.1
> >   retrieving revision 1.2
> >   diff -u -r1.1 -r1.2
> >   --- NWGNUmakefile	1 Mar 2002 22:25:26 -0000	1.1
> >   +++ NWGNUmakefile	27 Mar 2002 23:51:50 -0000	1.2
> >   @@ -238,6 +238,7 @@
> >    # Paths must all use the '/' character
> >    #
> >    FILES_lib_objs = \
> >   +	$(OBJDIR)/apr_atomic.o \
> >    	$(OBJDIR)/apr_cpystrn.o \
> >    	$(OBJDIR)/apr_fnmatch.o \
> >    	$(OBJDIR)/apr_getpass.o \
> >   @@ -317,6 +318,10 @@
> >    #
> >    # Any specialized rules here
> >    #
> >   +
> >   +$(OBJDIR)/%.o: atomic/netware/%.c $(OBJDIR)\cc.opt
> >   +	@echo Compiling $<
> >   +	$(CC) atomic\netware\$(<F) -o=$(OBJDIR)\$(@F)
> > @$(OBJDIR)\cc.opt 
> >    
> >    $(OBJDIR)/%.o: strings/%.c $(OBJDIR)\cc.opt
> >    	@echo Compiling $<
> >   
> >   
> >   
> >   1.4       +1 -0      apr/build/nw_export.inc
> >   
> >   Index: nw_export.inc
> >  
> > ==================================================================
> > = 
> >   RCS file: /home/cvs/apr/build/nw_export.inc,v
> >   retrieving revision 1.3
> >   retrieving revision 1.4
> >   diff -u -r1.3 -r1.4
> >   --- nw_export.inc	20 Feb 2002 19:58:57 -0000	1.3
> >   +++ nw_export.inc	27 Mar 2002 23:51:50 -0000	1.4
> >   @@ -10,6 +10,7 @@
> >    #undef APR_DECLARE_DATA
> >    
> >    /* Preprocess all of the standard APR headers. */
> >   +#include "apr_atomic.h"
> >    #include "apr_compat.h"
> >    #include "apr_dso.h"
> >    #include "apr_errno.h"
> >   
> >   
> >   
> >   1.21      +1 -1      apr/include/apr_atomic.h
> >   
> >   Index: apr_atomic.h
> >  
> > ==================================================================
> > = 
> >   RCS file: /home/cvs/apr/include/apr_atomic.h,v
> >   retrieving revision 1.20
> >   retrieving revision 1.21
> >   diff -u -r1.20 -r1.21
> >   --- apr_atomic.h	22 Mar 2002 18:51:07 -0000	1.20
> >   +++ apr_atomic.h	27 Mar 2002 23:51:51 -0000	1.21
> >   @@ -176,7 +176,7 @@
> >    #define apr_atomic_t unsigned long
> >    
> >    #define apr_atomic_add(mem, val)     atomic_add(mem,val)
> >   -#define apr_atomic_dec(mem)          atomic_dec(mem)
> >   +APR_DECLARE(int) apr_atomic_dec(apr_atomic_t *mem);
> >    #define apr_atomic_inc(mem)          atomic_inc(mem)
> >    #define apr_atomic_set(mem, val)     (*mem = val)
> >    #define apr_atomic_read(mem)         (*mem)
> >   
> >   
> >   
> >   1.1                  apr/atomic/netware/apr_atomic.c
> >   
> >   Index: apr_atomic.c
> >  
> > ==================================================================
> > = 
> >   /* 
> > ==================================================================
> > == 
> >    * The Apache Software License, Version 1.1
> >    *
> >    * Copyright (c) 2000-2002 The Apache Software Foundation.  
> > All rights
> >    * reserved.
> >    *
> >    * Redistribution and use in source and binary forms, with 
> > or without
> >    * modification, are permitted provided that the following 
> > conditions
> >    * are met:
> >    *
> >    * 1. Redistributions of source code must retain the above
> > copyright 
> >    *    notice, this list of conditions and the following
> > disclaimer. 
> >    *
> >    * 2. Redistributions in binary form must reproduce the 
> > above copyright
> >    *    notice, this list of conditions and the following 
> > disclaimer in
> >    *    the documentation and/or other materials provided with
> > the 
> >    *    distribution.
> >    *
> >    * 3. The end-user documentation included with the
> > redistribution, 
> >    *    if any, must include the following acknowledgment:
> >    *       "This product includes software developed by the
> >    *        Apache Software Foundation (http://www.apache.org/)."
> >    *    Alternately, this acknowledgment may appear in the 
> > software itself,
> >    *    if and wherever such third-party acknowledgments 
> > normally appear.
> >    *
> >    * 4. The names "Apache" and "Apache Software Foundation" must
> >    *    not be used to endorse or promote products derived from
> > this 
> >    *    software without prior written permission. For written
> >    *    permission, please contact apache@apache.org.
> >    *
> >    * 5. Products derived from this software may not be called 
> > "Apache",
> >    *    nor may "Apache" appear in their name, without prior
> > written 
> >    *    permission of the Apache Software Foundation.
> >    *
> >    * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR
> > IMPLIED 
> >    * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
> > WARRANTIES 
> >    * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
> >    * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE
> > FOUNDATION OR 
> >    * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
> > INCIDENTAL, 
> >    * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
> > NOT 
> >    * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
> > LOSS OF 
> >    * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
> > CAUSED AND
> >    * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
> > LIABILITY,
> >    * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
> > ANY WAY OUT
> >    * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
> > POSSIBILITY OF
> >    * SUCH DAMAGE.
> >    * 
> > ==================================================================
> > == 
> >    *
> >    * This software consists of voluntary contributions made by
> > many 
> >    * individuals on behalf of the Apache Software Foundation. 
> >  For more
> >    * information on the Apache Software Foundation, please see
> >    * <http://www.apache.org/>.
> >    */
> >   
> >   
> >   #include "apr.h"
> >   #include "apr_lock.h"
> >   #include "apr_thread_mutex.h"
> >   #include "apr_atomic.h"
> >   
> >   #if APR_HAS_THREADS
> >   
> >   #if defined(APR_ATOMIC_NEED_DEFAULT)  || 
> > defined(APR_ATOMIC_NEED_CAS_DEFAULT)
> >   
> >   #define NUM_ATOMIC_HASH 7
> >   /* shift by 2 to get rid of alignment issues */
> >   #define ATOMIC_HASH(x) (int)(((long)x>>2)%NUM_ATOMIC_HASH)
> >   static apr_thread_mutex_t **hash_mutex;
> >   
> >   apr_status_t apr_atomic_init(apr_pool_t *p )
> >   {
> >       int i;
> >       apr_status_t rv;
> >       hash_mutex =apr_palloc(p,sizeof(apr_thread_mutex_t*) * 
> > NUM_ATOMIC_HASH);
> >       for (i=0;i<NUM_ATOMIC_HASH;i++) w{
> >           rv = apr_thread_mutex_create(&(hash_mutex[i]), 
> > APR_THREAD_MUTEX_DEFAULT, p);
> >           if (rv != APR_SUCCESS)
> >              return rv;
> >       }
> >       return APR_SUCCESS;
> >   }
> >   #endif /* APR_ATOMIC_NEED_DEFAULT ||
> > APR_ATOMIC_NEED_CAS_DEFAULT */ 
> >   
> >   int apr_atomic_dec(apr_atomic_t *mem) 
> >   {
> >       atomic_inc(mem);
> >       return *mem; 
> >   }
> >   
> >   #if defined(APR_ATOMIC_NEED_CAS_DEFAULT)
> >   
> >   apr_uint32_t apr_atomic_cas(volatile apr_uint32_t *mem,long 
> > with, long cmp)
> >   {
> >       apr_thread_mutex_t *lock = hash_mutex[ATOMIC_HASH(mem)];
> >       long prev;
> >   
> >       if (apr_thread_mutex_lock(lock) == APR_SUCCESS) {
> >           prev = *(long*)mem;
> >           if ( prev == cmp) {
> >               *(long*)mem = with;
> >           }
> >           apr_thread_mutex_unlock(lock);
> >           return prev;
> >       }
> >       return *(long*)mem;
> >   }
> >   #endif /* APR_ATOMIC_NEED_CAS_DEFAULT */
> >   
> >   
> >   #endif /* APR_HAS_THREADS */
> >   
> >   
> >   
> > 
> 
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