Обсуждение: pgkill on win32
I'm wondering if the mechanism used for sending signals between postmaster processes on Win32 is much more heavyweight that is necessary. Is there a reason not to call OpenThread on the target postmaster's thread id, and then use QueueUserAPC to execute a 'signal handler' method on it? (Or Terminate Thread for 'extreme' cases). I don't think its entirely trivial because it would be better to cache the handles for a short time rather than Open/Queue/Close each time, so it may still be necessary to have a background thread that checks the handles are not signalled and closes them if they are. But signal delivery could be somewhat faster. Haven't tried it - but I can't help thinking that the named pipe service is a bit heavyweight. James
James Mansion wrote: > I'm wondering if the mechanism used for sending signals between > postmaster processes on Win32 is much more heavyweight that is > necessary. > > Is there a reason not to call OpenThread on the target postmaster's > thread id, and then use QueueUserAPC to execute a 'signal handler' > method on it? (Or Terminate Thread for 'extreme' cases). Yes. We used to use APCs, but touching anything remotely related to Winsock from an APC is not supported... We had a lot of trouble with it initially, and it took a long support case with Microsoft PSS to figure out what was broken, because this being unsupported was not properly documented. > Haven't tried it - but I can't help thinking that the named pipe > service is a bit heavyweight. It certainly is ;-) We could probably find something more efficient, but APCs are not the one. //Magnus
Magnus Hagander wrote: > Yes. We used to use APCs, but touching anything remotely related to > Winsock from an APC is not supported... We had a lot of trouble with it > By implication you'd be doing socket'y stuff from the signal handler on UNIX? Scary. I was assuming it would be used to signal an event that would release the main thread and then do the real work there. I suppose by implication you can't knock a thread out of select from the APC? Though, presumably, you could hand over the request to a waiting application thread and *that* would have full WinSock access. I can help feeling that the eventselect mechanism is the one to use, not the crappy bsd select emulation. > initially, and it took a long support case with Microsoft PSS to figure > out what was broken, because this being unsupported was not properly > documented. > Indeed. And its a very odd limitation given the way that APCs are used with completion ports. Did any sort of reference get written to the knowledge base for this, do you know? > It certainly is ;-) We could probably find something more efficient, > but APCs are not the one. > The concern I have isn't so much that the mechanism might be a bit ugly, but the synchronous delivery and the scheduling gymnastics implied..
James Mansion wrote: > Magnus Hagander wrote: > > Yes. We used to use APCs, but touching anything remotely related to > > Winsock from an APC is not supported... We had a lot of trouble > > with it > By implication you'd be doing socket'y stuff from the signal handler > on UNIX? Scary. Uh, sorry, got that explained backwards. The problem is when winsock operations are interrupted by APCs. See: http://archives.postgresql.org/pgsql-hackers-win32/2004-04/msg00013.php > I was assuming it would be used to signal an event that would release > the main > thread and then do the real work there. > > I suppose by implication you can't knock a thread out of select from > the APC? Not only that, but you may corrupt internal winsock structures if you try. As stated, one major issue is that we have third-party libs calling the winsock functions directly (SSL and Kerberos come to mind - the GSSAPI code specifically does not do this). For SSL, I'd like to eventually rewrite it to make sure *we* call the send and receive functions and just use the library to encrypt buffers, which should make things a bit safer in that regard. > I can help feeling that the eventselect mechanism is the one to use, > not the crappy bsd select emulation. The original design, which is what is there now, was written to make sure we made as little change as possible to the backend code itself, and instead implemented portability layers. I think now that the port is more mature, if we need to make some smaller changes around say the select loop processing, we can do that - as long as we're careful. But we certainly don't want to do anything that'll require more or less global changes around the code. > > initially, and it took a long support case with Microsoft PSS to > > figure out what was broken, because this being unsupported was not > > properly documented. > > > Indeed. And its a very odd limitation given the way that APCs are > used with completion ports. > Did any sort of reference get written to the knowledge base for this, > do you know? There was one written, AFIAK, but I don't remember the number or can't find it right now. It may well be that it's premier only. Also, it only applied to traditional sockets API calls, and not "native" Winsock2 calls. But see above about SSL. > > It certainly is ;-) We could probably find something more efficient, > > but APCs are not the one. > > > The concern I have isn't so much that the mechanism might be a bit > ugly, but the synchronous > delivery and the scheduling gymnastics implied.. Right. //Magnus
Magnus Hagander wrote: > The problem is when winsock operations are interrupted by APCs. > > See: > http://archives.postgresql.org/pgsql-hackers-win32/2004-04/msg00013.php > Whoa! Indeed, that's a bit sucky because they really aren't documented as interruptible. In this case though I see not material problem with going back to APCs. At the moment you deliver to a pipe server thread with a pipe RPC. I can't see why you cannot deliver to a signal handling thread with the APC - the published {thread-id,function} tuple does not need to refer to the main thread for the process. This would de-synchronize the delivery but make a relatively small change since that background thread could deliver to the main thread the same way it does now. If there were any desire to provide a MT-aware postmaster, the same technique of masking signals except on a signal thread might apply. James
On Mon, Apr 21, 2008 at 09:47:02AM +0200, Magnus Hagander wrote: > Uh, sorry, got that explained backwards. > The problem is when winsock operations are interrupted by APCs. > > See: > http://archives.postgresql.org/pgsql-hackers-win32/2004-04/msg00013.php WRT this bit: > (1) carries a big problem - if we do this, we can *not* support SSL > on win32, because it uses recv() and send() internally (inside the > openssl library). Therefor, I don't think (1) is really an option - > at least not in the long run. openssl does not have to use recv/send, that's what the BIO infrastructure is for. The current backend code already constructs BIOs for reading to support interrupting (see my_sock_read), so you could replace the read with any functions you wanted. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Please line up in a tree and maintain the heap invariant while > boarding. Thank you for flying nlogn airlines.
Martijn van Oosterhout wrote: > On Mon, Apr 21, 2008 at 09:47:02AM +0200, Magnus Hagander wrote: > > Uh, sorry, got that explained backwards. > > The problem is when winsock operations are interrupted by APCs. > > > > See: > > http://archives.postgresql.org/pgsql-hackers-win32/2004-04/msg00013.php > > WRT this bit: > > (1) carries a big problem - if we do this, we can *not* support SSL > > on win32, because it uses recv() and send() internally (inside the > > openssl library). Therefor, I don't think (1) is really an option - > > at least not in the long run. > > openssl does not have to use recv/send, that's what the BIO > infrastructure is for. The current backend code already constructs > BIOs for reading to support interrupting (see my_sock_read), so you > could replace the read with any functions you wanted. Yes, it's on my TODO list to do just that. Unless this means you are volunteering to do it? ;) //Magnus
James Mansion wrote: > Magnus Hagander wrote: > > The problem is when winsock operations are interrupted by APCs. > > > > See: > > http://archives.postgresql.org/pgsql-hackers-win32/2004-04/msg00013.php > > > Whoa! Indeed, that's a bit sucky because they really aren't > documented as interruptible. > > In this case though I see not material problem with going back to > APCs. At the moment you > deliver to a pipe server thread with a pipe RPC. I can't see why you > cannot deliver to a > signal handling thread with the APC - the published > {thread-id,function} tuple does not need > to refer to the main thread for the process. This would > de-synchronize the delivery but make > a relatively small change since that background thread could deliver > to the main thread the > same way it does now. Good point. I see no reason not to be able to do that, agreed. Once we accepted using a second thread for it, that opportunity is certainly there. You interested in trying to code up a patch to verify that? ;) > If there were any desire to provide a MT-aware postmaster, the same > technique of masking > signals except on a signal thread might apply. Define MT-aware :-) It's certainly MT-aware in the fact that it's already MT... But there is no interest in making the actual backends launch as threads in the postmaster - at least not currently. //Magnus
Magnus Hagander wrote: > You interested in trying to code up a patch to verify that? ;) > > Practical reality says that I won't get to this before the next version of Windows is released. I don't want to promise something I can't deliver. >> If there were any desire to provide a MT-aware postmaster, the same >> technique of masking >> signals except on a signal thread might apply. >> > > Define MT-aware :-) It's certainly MT-aware in the fact that it's > already MT... But there is no interest in making the actual backends > launch as threads in the postmaster - at least not currently. > I seem to remember being slapped about for daring to suggest using a threaded embedded language even if only one thread calls into the core, on the ground that the signals might not go to the right thread. So I'm assuming that a thread-aware build would generally mask async signals and wait for them in a specific thread in sigwait, which would effectively match the Win32 model (for a threaded build). On the other hand, I'd normally regard signals as the work of the devil and prefer to send a wakeup via some other IPC, for pretty much that reason, but there you go. James
James Mansion wrote: > Magnus Hagander wrote: > > You interested in trying to code up a patch to verify that? ;) > > > > > Practical reality says that I won't get to this before the next > version of Windows is released. > I don't want to promise something I can't deliver. :-) If you want to throw me some code-snippet-ideas off-list that's not ready for an actual patch, be my guest - and maybe I can put something together. > >> If there were any desire to provide a MT-aware postmaster, the > >> same technique of masking > >> signals except on a signal thread might apply. > >> > > > > Define MT-aware :-) It's certainly MT-aware in the fact that it's > > already MT... But there is no interest in making the actual backends > > launch as threads in the postmaster - at least not currently. > > > I seem to remember being slapped about for daring to suggest using a > threaded embedded > language even if only one thread calls into the core, on the ground > that the signals might not > go to the right thread. So I'm assuming that a thread-aware build > would generally mask async > signals and wait for them in a specific thread in sigwait, which > would effectively match the > Win32 model (for a threaded build). That is something different than a threaded build, though ;-) You're probably more likely to get that to happen - though maybe not by much... //Magnus