Here is some information I have gathered. We have a writer thread connection called A and a reader called B, another reader called C.
A is writing B is waiting on A with pBlockingConnection = A, and pUnlockConnection A A is Now done, A is waiting on B with pBlockingConnection = B and pUnlockConnection B B is now done but never goes to check to see if any connections are waiting to be unblocked, sqlite3ConnectionUnlocked never gets called. I have a print out every time it gets called with the connection which calls it. C then wants to read and has a pBlockingConnection = B and pUnlockConnection = B. And all the connections are then locked up. This information was gathered from pUnlockConnection and pBlockingConnection and by examining the blocked list. All writes are done using "BEGIN IMMEDIATE TRANSACTION" Owen On 9 July 2013 12:51, Dan Kennedy <danielk1...@gmail.com> wrote: > On 07/09/2013 06:41 PM, Owen Haynes wrote: > >> I have been using a debugger to look at pBlockedConnection and >> pUnlockConnection >> also added some extra print statements to the code, sqlite is also >> compiled >> with debug enabled, and no asserts seem to get triggered. >> > > > How do you know A has finished? Does "PRAGMA lock_status" > indicate that it is holding no locks at all? > > So in "deadlock 1", when you have: > > > Connection A is has finished > Connection B is waiting on Connection A > Connection C is waiting on Connection B > > Then the following are all true? > > B->pUnlockConnection = A; > B->pBlockingConnection = A; > C->pUnlockConnection = B; > C->pBlockingConnection = B; > > Are both B and C in the linked list that starts at global > variable sqlite3BlockedList (and connected by pNextBlocked)? > > Dan. > > > > > > >> Owen >> >> >> >> >> On 9 July 2013 11:20, Dan Kennedy <danielk1...@gmail.com> wrote: >> >> On 07/09/2013 04:08 PM, Dan Kennedy wrote: >>> >>> On 06/20/2013 03:20 PM, Owen Haynes wrote: >>>> >>>> Hello, >>>>> >>>>> I am currently having some problems with the unlock notify and getting >>>>> in a >>>>> state of deadlock. >>>>> >>>>> I am using code based on >>>>> http://www.sqlite.org/unlock_****notify.html<http://www.sqlite.org/unlock_**notify.html> >>>>> <http://www.**sqlite.org/unlock_notify.html<http://www.sqlite.org/unlock_notify.html> >>>>> >**, >>>>> >>>>> with >>>>> the latest sqlite. >>>>> >>>>> The setup is as follows: >>>>> - WAL is on >>>>> - Multi Threaded is on >>>>> - Temp store is memory >>>>> - Database is stored in /dev/shm >>>>> - Synchronous is set as normal >>>>> - Multi-threading is on >>>>> - connection is set as SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | >>>>> SQLITE_OPEN_NOMUTEX | SQLITE_OPEN_SHAREDCACHE >>>>> >>>>> Unlock notify does work I can see my log messages printed when the >>>>> callback >>>>> is called but sometimes I can end up in the following dead lock >>>>> situation. >>>>> >>>>> Each connection is in its own thread >>>>> >>>>> *Deadlock 1* >>>>> Connection A is using database >>>>> Connection B is waiting on Connection A >>>>> Connection C is waiting on Connection B >>>>> >>>>> Connection A is has finished >>>>> Connection B is waiting on Connection A >>>>> Connection C is waiting on Connection B >>>>> >>>>> How do you know this is what is happening? Are you looking >>> at the sqlite3.pBlockedConnection and sqlite3.pUnlockConnection >>> pointers in a debugger? Or some other method? >>> >>> Also, if this is easy to reproduce, try running with SQLITE_DEBUG >>> defined. This will enable some complex asserts that check for >>> various problems in the unlock-notify code. >>> >>> Dan. >>> >>> >>> >>> >>> >>> >>> *Deadlock 2* >>>>> Connection A is using database >>>>> Connection B is waiting on Connection A >>>>> Connection C is waiting on Connection A >>>>> >>>>> Connection A is has finished >>>>> Connection B is waiting on Connection A >>>>> Connection C is waiting on Connection A >>>>> >>>>> For some reason sometimes the notify callback does not get issued and >>>>> end >>>>> up with 2 threads waiting for the callback back to be issued. >>>>> >>>>> Connection B is a writer thread the others only read. >>>>> >>>>> Any ideas? >>>>> >>>>> Are you handling the case where the xNotify callback is invoked by >>>> sqlite3_unlock_notify() before it returns? >>>> >>>> Dan. >>>> >>>> >>>> ______________________________****_________________ >>> sqlite-users mailing list >>> sqlite-users@sqlite.org >>> http://sqlite.org:8080/cgi-****bin/mailman/listinfo/sqlite-****users<http://sqlite.org:8080/cgi-**bin/mailman/listinfo/sqlite-**users> >>> <http://sqlite.org:8080/**cgi-bin/mailman/listinfo/**sqlite-users<http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users> >>> > >>> >>> ______________________________**_________________ >> sqlite-users mailing list >> sqlite-users@sqlite.org >> http://sqlite.org:8080/cgi-**bin/mailman/listinfo/sqlite-**users<http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users> >> > > ______________________________**_________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-**bin/mailman/listinfo/sqlite-**users<http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users> > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
