Uploaded image for project: 'Qt'
  1. Qt
  2. QTBUG-41421

Exponential memory leak in V4 Array.

    XMLWordPrintable

Details

    • Bug
    • Resolution: Done
    • P1: Critical
    • 5.4.0 RC
    • 5.3.2
    • None
    • Linux pc 3.16.2-1-ARCH #1 SMP PREEMPT Sat Sep 6 13:12:51 CEST 2014 x86_64 GNU/Linux

    Description

      I attached a trivial testcase to reproduce the leak.

      Short version here:

          var queue = [];
          for (var i = 0; i < 1000; i++) {
              queue.unshift(5);
              queue.splice(0, 1);
          }
      

      This code creates an array, and then adds an element to it and cuts out an array of length 1 starting from the element number 0. The last two steps are repeated 1000 times.

      V4 utilizes all available memory and crashes.

      300 iterations produce ~200 MiB memory usage for me.
      350 iterations — ~1.5 GiB.
      360 iterations — ~3.1 GiB.

      Update:

      Actually, unshift-pop produces the same behavior (memleak), unshift-shift does not.

      unshift-pop — bad
      unshift-splice — bad
      unshift-shift — ok
      push-pop — ok
      push-splice — ok
      push-shift — ok

      So, the memleak could be reproduced even with

      var queue = [];
      for (var i = 0; i < 1000; i++) {
          queue.unshift(5);
          queue.pop();
      }
      

      Attachments

        1. memoryCrash2.qml
          0.5 kB
        2. memoryCrash3.qml
          0.2 kB
        3. memoryCrash4.qml
          0.2 kB
        4. memoryCrash5.qml
          0.2 kB
        5. qmlleak.200.massif.out
          595 kB
        6. qmlleak.310.callgrind.out
          1.91 MB
        7. qmlleak.310.massif.out
          155 kB

        Issue Links

          For Gerrit Dashboard: QTBUG-41421
          # Subject Branch Project Status CR V

          Activity

            People

              laknoll Lars Knoll
              chalker Сковорода Никита
              Votes:
              2 Vote for this issue
              Watchers:
              9 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved:

                Gerrit Reviews

                  There are no open Gerrit changes