Thread: Re: [PATCHES] Compiling libpq with VisualC
[ Thread moved to hackers and win32.]
Andreas Pflug wrote:
> Bruce Momjian wrote:
>
> >
> >
> >Agreed. My pthread book says pthread_mutex_init() should be called only
> >once, and we have to guarantee that. If the Windows implentation allows
> >it to be called multiple times, just create a function to be called only
> >by Win32 that does that and leave the Unix safe.
> >
> >
> >
> Ok, so here's the win32 workaround with the unix stuff left untouched.
> There's no memory interlocking api in win32 that wouldn't need some
> initializing api call itself, so we'd have to go for assembly level
> test-and-set code or introduce a mandatory global libpq initializing
> api. Considering the probably quite low usage of kerberos/ssl together
> with threads under win32, and the very low probability of two
> threads/processors (!) trying to initiate a connection at the same time,
> it doesn't seem to be worth the compiler hassle with assembly inline.
What is the recommended way to create mutex objects (CreateMutex) from
Win32 libraries? There must be a clean way like there is in pthreads.
---------------------------------------------------------------------------
In the patch Win32, pthread_mutex_init() == CreateMutex():
+#ifndef WIN32
static pthread_mutex_t singlethread_lock = PTHREAD_MUTEX_INITIALIZER;
+#else
+ static pthread_mutex_t singlethread_lock;
+ static int mutex_initialized = 0;
+ if (!mutex_initialized)
+ {
+ mutex_initialized = 1;
+ pthread_mutex_init(&singlethread_lock, NULL);
+ }
+#endif
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian wrote: > >What is the recommended way to create mutex objects (CreateMutex) from >Win32 libraries? There must be a clean way like there is in pthreads. > It's having a central one-time called routine executing CreateMutex. This can be DllMain, *if* used as DLL, but that's certainly no solution for static linkage. This would require some PQinitThreadStuff() routine, which may be called only once (and ultimately can't check for that itself, if you don't trust a static var). Regards, Andreas
Andreas Pflug wrote: > Bruce Momjian wrote: > > > > >What is the recommended way to create mutex objects (CreateMutex) from > >Win32 libraries? There must be a clean way like there is in pthreads. > > > > It's having a central one-time called routine executing CreateMutex. > This can be DllMain, *if* used as DLL, but that's certainly no solution > for static linkage. This would require some PQinitThreadStuff() routine, > which may be called only once (and ultimately can't check for that > itself, if you don't trust a static var). Ewe. Well, I am not excited about adding a thread capability for Win32 that isn't 100% guaranteed to work. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
>
> [ Thread moved to hackers and win32.]
>
> Andreas Pflug wrote:
>> Bruce Momjian wrote:
>>
>> >
>> >
>> >Agreed. My pthread book says pthread_mutex_init() should be called
>> only
>> >once, and we have to guarantee that. If the Windows implentation
>> allows
>> >it to be called multiple times, just create a function to be called
>> only
>> >by Win32 that does that and leave the Unix safe.
>> >
>> >
>> >
>> Ok, so here's the win32 workaround with the unix stuff left untouched.
>> There's no memory interlocking api in win32 that wouldn't need some
>> initializing api call itself, so we'd have to go for assembly level
>> test-and-set code or introduce a mandatory global libpq initializing
>> api. Considering the probably quite low usage of kerberos/ssl together
>> with threads under win32, and the very low probability of two
>> threads/processors (!) trying to initiate a connection at the same time,
>> it doesn't seem to be worth the compiler hassle with assembly inline.
>
> What is the recommended way to create mutex objects (CreateMutex) from
> Win32 libraries? There must be a clean way like there is in pthreads.
A mutex is inherently a global object. CreateMutex(NULL, FALSE, NULL) will
return a handle to an unowned mutex.
>
> ---------------------------------------------------------------------------
>
> In the patch Win32, pthread_mutex_init() == CreateMutex():
>
> +#ifndef WIN32
> static pthread_mutex_t singlethread_lock =
> PTHREAD_MUTEX_INITIALIZER;
> +#else
> + static pthread_mutex_t singlethread_lock;
> + static int mutex_initialized = 0;
> + if (!mutex_initialized)
> + {
> + mutex_initialized = 1;
> + pthread_mutex_init(&singlethread_lock, NULL);
> + }
> +#endif
>
> --
> Bruce Momjian | http://candle.pha.pa.us
> pgman@candle.pha.pa.us | (610) 359-1001
> + If your life is a hard drive, | 13 Roberts Road
> + Christ can be your backup. | Newtown Square, Pennsylvania
> 19073
>
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>
pgsql@mohawksoft.com wrote: > > > > [ Thread moved to hackers and win32.] > > > > Andreas Pflug wrote: > >> Bruce Momjian wrote: > >> > >> > > >> > > >> >Agreed. My pthread book says pthread_mutex_init() should be called > >> only > >> >once, and we have to guarantee that. If the Windows implentation > >> allows > >> >it to be called multiple times, just create a function to be called > >> only > >> >by Win32 that does that and leave the Unix safe. > >> > > >> > > >> > > >> Ok, so here's the win32 workaround with the unix stuff left untouched. > >> There's no memory interlocking api in win32 that wouldn't need some > >> initializing api call itself, so we'd have to go for assembly level > >> test-and-set code or introduce a mandatory global libpq initializing > >> api. Considering the probably quite low usage of kerberos/ssl together > >> with threads under win32, and the very low probability of two > >> threads/processors (!) trying to initiate a connection at the same time, > >> it doesn't seem to be worth the compiler hassle with assembly inline. > > > > What is the recommended way to create mutex objects (CreateMutex) from > > Win32 libraries? There must be a clean way like there is in pthreads. > > A mutex is inherently a global object. CreateMutex(NULL, FALSE, NULL) will > return a handle to an unowned mutex. Yes, but consider that two threads could both call it, with one perhaps using the first value, and the second overwriting the first. Obviously not something we want. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
pgsql@mohawksoft.com wrote:
>>
>>What is the recommended way to create mutex objects (CreateMutex) from
>>Win32 libraries? There must be a clean way like there is in pthreads.
>>
>>
>
>A mutex is inherently a global object. CreateMutex(NULL, FALSE, NULL) will
>return a handle to an unowned mutex.
>
>
>
That's not the problem. Under pthread, it's possible to initialize a
mutex from compile time:
static pthread_mutex_t init_mutex = PTHREAD_MUTEX_INITIALIZER;
This means that the mutex is immediately valid, no races with the
initialization. I couldn't find an equivalent Win32 feature.
--
Manfred