René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Updating progress pane using timer causes race condition that would randomly crash powershell","articleBody":"With PR #2640, a timer is used to trigger updating progress pane every 100 ms to improve progress record rendering performance (commit: https://github.com/PowerShell/PowerShell/commit/760a9c2997148f32a0b763165a32647abe49b985). Before the change, `_progPane.Show` and `_pendingProgress.Update` used to be called on the same thread, and now they will be called on different threads. This causes race conditions -- **for all type members that are used by both methods, they might be changed at the same time and the states may be corrupted.**\r\n\r\nThe screenshot below is from a recent CI build on master branch. The exception was raised from [RenderHelper](https://github.com/PowerShell/PowerShell/blob/master/src/Microsoft.PowerShell.ConsoleHost/host/msh/PendingProgress.cs#L763), and that was because it was actually enumerating over `PendingProgress._topLevelNodes` and at the same time new node was being added to/removed from `_topLevelNodes` by [Update](https://github.com/PowerShell/PowerShell/blob/master/src/Microsoft.PowerShell.ConsoleHost/host/msh/PendingProgress.cs#L60).\r\n\r\n![image](https://cloud.githubusercontent.com/assets/127450/20699550/bd1d52e6-b5bc-11e6-862d-cf3a302d8fe7.png)\r\n\r\n\r\n/cc @iSazonov @lzybkr ","author":{"url":"https://github.com/daxian-dbw","@type":"Person","name":"daxian-dbw"},"datePublished":"2016-11-29T07:01:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/2800/PowerShell/issues/2800"}