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MultiThreading Dataset Strange ProblemI have a multithreaded vb .net app that uses several datasets; all writes to
the datasets are synchronized using synclocks, no synchronization is used for reads. No items or rows in the sets are being deleted, just updating values. At random times it will break into the debugger with index outside of the bounds of the array exceptions, when it does this the variable used for the row index says it is zero which was normal and it even showed the correct value for the item in the dataset. For example: If CInt(CMPDAT.Tables(0).Rows(i).Item("ID")) = 0 Then it showed that i was equal to zero and the value for "ID" was equal to one which it should have been, but it still threw the exception? Any help would be greatly appreciated.
Show quote
On Feb 2, 2:48 pm, "Matt Barley" <mbar***@fessystems.com> wrote: Hi,> I have a multithreaded vb .net app that uses several datasets; all writes to > the datasets are synchronized using synclocks, no synchronization is used > for reads. No items or rows in the sets are being deleted, just updating > values. At random times it will break into the debugger with index outside > of the bounds of the array exceptions, when it does this the variable used > for the row index says it is zero which was normal and it even showed the > correct value for the item in the dataset. For example: > > If CInt(CMPDAT.Tables(0).Rows(i).Item("ID")) = 0 Then > > it showed that i was equal to zero and the value for "ID" was equal to one > which it should have been, but it still threw the exception? > > Any help would be greatly appreciated. Well, the documentation for a DataSet says, "This type is safe for multithreaded read operations. You must synchronize any write operations", but it's not clear exactly what that means. Does it mean the data structure is thread-safe for one writer and multiple readers like the Hashtable or is it thread-safe for multiple readers only when there are no writers? I'm wondering if it's the later because if it behaved like the Hashtable then I would expect the documentation to read like it too. When in doubt *always* synchronize multithreaded operations even if they are just reads. Ya know...some data structures actually modify themselves during reads (splay trees). And of course there's always the problem of the reading thread seeing current state when synchronization isn't used. Brian Thanks Brian for the info. It seems that I only see the problem when i run
the program in the vs debugger; running the app on our target device for several days now and it hasn't happened? Not sure what the debugger could be doing to cause this. Now i am running the app on my development machine outside the debugger and haven't seen any exceptions. Show quote "Brian Gideon" <briangid***@yahoo.com> wrote in message news:1170455384.115639.142900@m58g2000cwm.googlegroups.com... > On Feb 2, 2:48 pm, "Matt Barley" <mbar***@fessystems.com> wrote: >> I have a multithreaded vb .net app that uses several datasets; all writes >> to >> the datasets are synchronized using synclocks, no synchronization is used >> for reads. No items or rows in the sets are being deleted, just updating >> values. At random times it will break into the debugger with index >> outside >> of the bounds of the array exceptions, when it does this the variable >> used >> for the row index says it is zero which was normal and it even showed the >> correct value for the item in the dataset. For example: >> >> If CInt(CMPDAT.Tables(0).Rows(i).Item("ID")) = 0 Then >> >> it showed that i was equal to zero and the value for "ID" was equal to >> one >> which it should have been, but it still threw the exception? >> >> Any help would be greatly appreciated. > > Hi, > > Well, the documentation for a DataSet says, "This type is safe for > multithreaded read operations. You must synchronize any write > operations", but it's not clear exactly what that means. Does it mean > the data structure is thread-safe for one writer and multiple readers > like the Hashtable or is it thread-safe for multiple readers only when > there are no writers? I'm wondering if it's the later because if it > behaved like the Hashtable then I would expect the documentation to > read like it too. > > When in doubt *always* synchronize multithreaded operations even if > they are just reads. Ya know...some data structures actually modify > themselves during reads (splay trees). And of course there's always > the problem of the reading thread seeing current state when > synchronization isn't used. > > Brian > > Thanks Brian for the info. It seems that I only see the problem when i Well, that's a recipe for disaster because it will happen outside the > run the program in the vs debugger; debugger. Eventually. Multi-threaded issues are typically nasty to resolve - but you already knew that. My first step would be to use the test and load pattern on the dataset, which you aren't doing. That won't fix the problem by the way. if(ds != null && ds.Table != null && ds.Table.Count > 0 && ds.Table[0].Rows.Count > 0) { //access safely } If you get an exception on that part of the code, you can safely say that the exception is not related to an index out of range, but more likely an access violation/locking issue. Try that first. -- Show quoteRegards, Alvin Bruney ------------------------------------------------------ Shameless author plug Excel Services for .NET is coming... OWC Black book on Amazon and www.lulu.com/owc "Matt Barley" <mbar***@fessystems.com> wrote in message news:O0NFAFzRHHA.4076@TK2MSFTNGP05.phx.gbl... > Thanks Brian for the info. It seems that I only see the problem when i > run the program in the vs debugger; running the app on our target device > for several days now and it hasn't happened? Not sure what the debugger > could be doing to cause this. Now i am running the app on my development > machine outside the debugger and haven't seen any exceptions. > > "Brian Gideon" <briangid***@yahoo.com> wrote in message > news:1170455384.115639.142900@m58g2000cwm.googlegroups.com... >> On Feb 2, 2:48 pm, "Matt Barley" <mbar***@fessystems.com> wrote: >>> I have a multithreaded vb .net app that uses several datasets; all >>> writes to >>> the datasets are synchronized using synclocks, no synchronization is >>> used >>> for reads. No items or rows in the sets are being deleted, just >>> updating >>> values. At random times it will break into the debugger with index >>> outside >>> of the bounds of the array exceptions, when it does this the variable >>> used >>> for the row index says it is zero which was normal and it even showed >>> the >>> correct value for the item in the dataset. For example: >>> >>> If CInt(CMPDAT.Tables(0).Rows(i).Item("ID")) = 0 Then >>> >>> it showed that i was equal to zero and the value for "ID" was equal to >>> one >>> which it should have been, but it still threw the exception? >>> >>> Any help would be greatly appreciated. >> >> Hi, >> >> Well, the documentation for a DataSet says, "This type is safe for >> multithreaded read operations. You must synchronize any write >> operations", but it's not clear exactly what that means. Does it mean >> the data structure is thread-safe for one writer and multiple readers >> like the Hashtable or is it thread-safe for multiple readers only when >> there are no writers? I'm wondering if it's the later because if it >> behaved like the Hashtable then I would expect the documentation to >> read like it too. >> >> When in doubt *always* synchronize multithreaded operations even if >> they are just reads. Ya know...some data structures actually modify >> themselves during reads (splay trees). And of course there's always >> the problem of the reading thread seeing current state when >> synchronization isn't used. >> >> Brian >> > >  |
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