<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div apple-content-edited="true"><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>Umm, no, we do not need this for pthreads, since the windowing on non-Windows system does not have the problem you describe. I think that a deeper understanding of the WinTrestle code is needed here. From reading the WinTrestle comments, it says that calls out to Windows are performed by a special thread that has no locks held. So, how can a call-back from Windows (presumably within the same thread) manage to be in a state where the thread has locks. It sounds like there may be something broken in the design of WinTrestle, but this is NOT a motivation to complicate the Thread interface. I suggest that effort be focused in WinTrestle rather than making a global hack that is not justified.</div></span></span></span></span></span></span></span></span></div></span> </div><br><div><div>On Aug 15, 2008, at 12:29 PM, Jay wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div class="hmmessage" style="font-size: 10pt; font-family: Tahoma; ">There is a case, trivial to hit, in WinTrestle that calls out to Windows with some locks held, Windows calls back into Trestle, Trestle attempts to acquire the locks again, and it dies.<br><br>It should be easy to implement...<br><br>All it takes to hit this in WinTrestle is to copy (as in copy/paste) twice in the same app.<br>My example was from the same control but that isn't necessary.<br>Just copy from one Trestle control and then copy from another and it hits.<br><br>A careful review might reveal that is safe to release the locks, call out, reacquire.<br>The comments indicate a general non-calling out with locks held, but the implementation does not quite agree.<br><br>pthread has this: PTHREAD_MUTEX_RECURSIVE<br>It's just bogus?<br><br>One lock type -- nonrecursive mutex -- is really all you need?<br><br>I assume a multi-reader/single-writer is also useful. In fact, a mutex can just be a reader/writer where everyone is a writer, though that might waste space (given that Windows now has a reader/writer lock that is just the size of a pointer, maybe not).<br><br>- Jay<br><br>> From:<span class="Apple-converted-space"> </span><a href="mailto:hosking@cs.purdue.edu">hosking@cs.purdue.edu</a><br>> To:<span class="Apple-converted-space"> </span><a href="mailto:jay.krell@cornell.edu">jay.krell@cornell.edu</a><br>> Date: Fri, 15 Aug 2008 11:41:23 +0100<br>> CC:<span class="Apple-converted-space"> </span><a href="mailto:m3commit@elegosoft.com">m3commit@elegosoft.com</a><br>> Subject: Re: [M3commit] CVS Update: cm3<br>><br>> I am unclear as to why this abstraction is needed for Windows threads<br>> when it is not needed for pthreads. Please explain.<br>><br>> On Aug 15, 2008, at 2:08 AM, Jay wrote:<br>><br>> ><br>> > We should probably add a new type Thread.RecursiveExclusiveLock? And<br>> > then just use that here?<br>> > The basic Win32 critical section is such a thing precisely. Not that<br>> > it is all that great. But it is widely used.<br>> > Vista adds the "SRWLock" which is a small read/write lock and maybe<br>> > reduced recursive functionality.<br>> > It is indeed small, just the size of a pointer, whereas a critical<br>> > section is fairly large.<br>> ><br>> > - Jay<br>> ><br>> ><br>> ><br>> > Date: Thu, 14 Aug 2008 20:11:19 -0400From:<span class="Apple-converted-space"> </span><a href="mailto:rcoleburn@scires.comTo">rcoleburn@scires.comTo</a>:<span class="Apple-converted-space"> </span><a href="mailto:jay.krell@cornell.edu">jay.krell@cornell.edu</a><br>> > ;<span class="Apple-converted-space"> </span><a href="mailto:jkrell@elego.de">jkrell@elego.de</a>;<span class="Apple-converted-space"> </span><a href="mailto:m3commit@elegosoft.comSubject">m3commit@elegosoft.comSubject</a>: Re: [M3commit] CVS<br>> > Update: cm3<br>> ><br>> > Jay:<br>> ><br>> > There is the abstraction of multiple concurrent "readers" but only<br>> > one "writer". I actually have such a module that I use sometimes in<br>> > my programs. The idea is one of acquiring/releasing read locks and<br>> > write locks. The difficulty here is in preventing starvation and<br>> > usually requires adherence to some rules (again rigor). By<br>> > starvation I mean that writers must wait for all readers to finish<br>> > before they get access, so if there is always at least one reader,<br>> > the writer will "starve" and never gain access.<br>> ><br>> > As for recursive locks, again that is usually indicative of a design<br>> > flaw. I did once implement a system that permitted the same thread<br>> > to acquire a lock multiple times, provided that it eventually<br>> > released the lock the same number of times that it acquired it. In<br>> > other words, after the first lock, subsequent locks by the same<br>> > thread just increment a counter. Then, unlocks decrement the<br>> > counter until it is zero with the final unlock actually releasing<br>> > the mutex.<br>> ><br>> > In the code you modified, you could implement such a scheme to<br>> > handle the recursive locks, provided that at some point the thread<br>> > releases for each lock. The Thread interface has the ability to<br>> > note the current thread (i.e., Thread.Self()). So you could make a<br>> > stack of locks by same thread. Other threads would have to block<br>> > until the first thread's lock stack was empty.<br>> ><br>> > For example:<br>> ><br>> > ACQUIRE: If resource available, lock resource mutex and put current<br>> > thread on granted stack. Otherwise, if current thread already on<br>> > granted stack, push it on stack again and let it proceed. Otherwise<br>> > (this is a new thread wanting access), so push this thread onto a<br>> > waiting stack and wait<br>><br><br></div></span></blockquote></div><br></body></html>