On 08/03/2018 01:52 AM, Jeremiah Breeden wrote: > I'm not following on how whether it is atomic helps in this case. Can you go > more into detail there? > > The issue I ran into (and I think the OP ran into) is that > > 1. Task A gets a cursor and saves it, > 2. does some process (either Ping or Close) > 3. Iterates the cursor and saves the new one. > 4. Repeats this in a loop until all cursors are checked > > but sometimes Task B deletes the element of that saved cursor while Task A is > at > step 2. Then when task A hits Step 3, the cursor is invalid and it throws an > exception. Prior to the bandaid I suggested, if that happened during the > "close" loop, it would completely deadlock the close process. The symptom for > my application was that when I hit the "terminate program" button, it wouldn't > terminate and future attempts to do so would not even try again. The OP was > seeing some different results, but I suspect it has to do with the cursors as > well. > > My understanding of Atomic in Ada is that it guarantees that writes/reads are > not interrupted and that they happen in the order specified. In this case, > the > problem isn't that the writes or reads are interrupted but that the map itself > is being modified while another task holds a cursor to it (thus making the > cursor invalid). If this happens during the Ping loop, then it simply aborts > the pinging process (maybe/maybe not detrimental). If it interrupts the Close > loop, then it (now) restarts the loop and tries again (before it deadlocked).
I meant atomic in its generic sense, not as aspect/pragma Atomic. If the loop is an atomic operation (provided by the PO), then the other task cannot interfere with it. During the Close loop, the program is ending (IIUC), so it doesn't matter how long it takes. For Ping, how long the loop takes might be an issue, but since it's only done once per minute, if there aren't too many connections, it might be acceptable. -- Jeff Carter "I like it when the support group complains that they have insufficient data on mean time to repair bugs in Ada software." Robert I. Eachus 91 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Gnoga-list mailing list Gnoga-list@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gnoga-list
