RE: [Xen-cim] Emailing: libxen.diff

["Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>]

Ewan,
It looks like if we can just do these inside _init and _fini (which are
functions called when the library is loaded and unloaded respectively),
we won't need to wory about MT-safeness. The OS won't unload the shared
library till everyone who's linked to it has unloaded.
Was there any specific reason why there were specific xen_init and
xen_fini calls created?

Raj

> -----Original Message-----
> From: Ewan Mellor [mailto:ewan@xxxxxxxxxxxxx] 
> Sent: Saturday, December 23, 2006 5:13 AM
> To: Subrahmanian, Raj
> Cc: xen-cim@xxxxxxxxxxxxxxxxxxx; Jim Fehlig
> Subject: Re: [Xen-cim] Emailing: libxen.diff
> 
> On Fri, Dec 22, 2006 at 10:00:49PM -0500, Subrahmanian, Raj wrote:
> 
> > This will MT-safe the xen_init and xen_fini calls, so that 
> we can do 
> > it once for each provider than for each call.
> 
> I don't think that this belongs in libxen, as that library 
> shouldn't add a dependency on libpthread unconditionally.  
> Can't you do this inside the provider?
> 
> Ewan.
> 
> > Raj
> >  <<libxen.diff>>
> 
> > diff -r 8348f40ba2b7 tools/libxen/Makefile
> > --- a/tools/libxen/Makefile Thu Dec 21 14:49:19 2006 +0000
> > +++ b/tools/libxen/Makefile Fri Dec 22 17:32:26 2006 -0500
> > @@ -27,7 +27,8 @@ CFLAGS = -Iinclude                     \
> >           -W -Wall -Wmissing-prototypes -Werror -std=c99 -O2 -fPIC
> >  
> >  LDFLAGS = $(shell xml2-config --libs) \
 > -          $(shell curl-config --libs)
> > +          $(shell curl-config --libs) \
> > +     -lpthread
> >  
> >  LIBXENAPI_HDRS = $(wildcard include/*.h)  LIBXENAPI_OBJS = 
> $(patsubst 
> > %.c, %.o, $(wildcard src/*.c)) diff -r 8348f40ba2b7 
> > tools/libxen/include/xen_common.h
> > --- a/tools/libxen/include/xen_common.h     Thu Dec 21 
> 14:49:19 2006 +0000
> > +++ b/tools/libxen/include/xen_common.h     Fri Dec 22 
> 17:32:26 2006 -0500
> > @@ -24,13 +24,13 @@
> >  #include <stddef.h>
> >  #include <stdint.h>
> >  #include <time.h>
> > -
> > +// The init and the fini really need to happen only once. 
> > +// The mutex will take care of that
> > +#include <pthread.h>
> >  #include "xen_host_decl.h"
> > -
> >  
> >  typedef bool (*xen_result_func)(const void *data, size_t len,
> >                                  void *result_handle);
> > -
> >  
> >  /**
> >   * len does not include a terminating \0.
> > diff -r 8348f40ba2b7 tools/libxen/src/xen_common.c
> > --- a/tools/libxen/src/xen_common.c Thu Dec 21 14:49:19 2006 +0000
> > +++ b/tools/libxen/src/xen_common.c Fri Dec 22 17:32:26 2006 -0500
> > @@ -43,6 +43,8 @@
> >  #define PERMISSIVE 1
> >  
> >  
> > +static pthread_mutex_t mutexUserCount=PTHREAD_MUTEX_INITIALIZER;
> > +static unsigned UserCount=0;
> >  static xmlXPathCompExprPtr responsePath = NULL;  static 
> > xmlXPathCompExprPtr faultPath = NULL;
> >  
> > @@ -111,23 +113,35 @@ void
> >  void
> >  xen_init(void)
> >  {
> > -    responsePath =
> > -        xmlXPathCompile(
> > -            BAD_CAST(
> > -                
> "/methodResponse/params/param/value/struct/member/value"));
> > -    faultPath =
> > -        xmlXPathCompile(
> > -            
> BAD_CAST("/methodResponse/fault/value/struct/member/value"));
> > +    pthread_mutex_lock(&mutexUserCount);
> > +    if (UserCount==0)
> > +    {
> > +           responsePath =
> > +           xmlXPathCompile(
> > +                   BAD_CAST(
> > +                   
> "/methodResponse/params/param/value/struct/member/value"));
> > +           faultPath =
> > +           xmlXPathCompile(
> > +                   
> BAD_CAST("/methodResponse/fault/value/struct/member/value"));
> > +    }
> > +    UserCount++;
> > +    pthread_mutex_unlock(&mutexUserCount);
> >  }
> >  
> >  
> >  void
> >  xen_fini(void)
> >  {
> > -    xmlXPathFreeCompExpr(responsePath);
> > -    xmlXPathFreeCompExpr(faultPath);
> > -    responsePath = NULL;
> > -    faultPath = NULL;
> > +    pthread_mutex_lock(&mutexUserCount);
> > +    UserCount--;
> > +    if (UserCount==0)
> > +    {
> > +        xmlXPathFreeCompExpr(responsePath);
> > +        xmlXPathFreeCompExpr(faultPath);
> > +        responsePath = NULL;
> > +        faultPath = NULL;
> > +    }
> > +    pthread_mutex_unlock(&mutexUserCount);
> >  }
> 
> > _______________________________________________
> > Xen-cim mailing list
> > Xen-cim@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-cim
> 
> 

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