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Set a Watch on Variables in Parallel Threads in Visual Studio (C#, Visual Basic, C++)

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In the Parallel Watch window, you can simultaneously display the values that one expression holds on multiple threads. Each row represents a thread that is running in an application, but a thread might be represented in multiple rows. More specifically, each row represents a function call whose function signature matches the function on the current stack frame. You can sort, reorder, remove, and group the items that are in the columns. You can flag, unflag, freeze (suspend), and thaw (resume) threads. The following columns are displayed in the Parallel Watch window:

  • The flag column, in which you can mark a thread that you want to pay special attention to.

  • The current thread column, in which a yellow arrow indicates the current thread (a green arrow with a curly tail indicates that a non-current thread has the current debugger context).

  • A configurable column that can display the machine, process, tile, task, and thread.

    Tip

    To display task information in the Parallel Watch window, you must first open the Task window.

  • The blank add watch columns, in which you can enter expressions to watch.

    Note

    Your computer might show different names or locations for some of the Visual Studio user interface elements in this article. You might be using a different edition of Visual Studio or different environment settings. For more information, see Personalize the IDE.

To display the Parallel Watch window

  1. Set a breakpoint in the code.

  2. On the menu bar, choose Debug, Start Debugging. Wait for the application to reach the breakpoint.

  3. On the menu bar, choose Debug, Windows, Parallel Watch, and then choose a watch window. You can open as many as four windows.

To add a watch expression

  • Select one of the blank add watch columns and then enter a watch expression.

To flag or unflag a thread

  • Select the flag column for the row (first column), or open the shortcut menu for the thread and choose Flag or Unflag.

To display only flagged threads

  • Choose the Show Only Flagged button in the upper-left corner of the Parallel Watch window.

To switch to another thread

  • Double-click the current thread column (second column). (Keyboard: Select the row and press Enter.)

To sort a column

  • Select the column heading.

To group threads

  • Open the shortcut menu for the Parallel Watch window, choose Group By, and then choose the appropriate submenu item.

To freeze or thaw threads

  • Open the shortcut menu for the row and choose Freeze or Thaw.

To export the data in the Parallel Watch window

  • Choose the Open in Excel button and then choose Open in Excel or Export to CSV.

To filter by a Boolean expression

  • Enter a Boolean expression in the Filter by Boolean Expression box. The debugger evaluates the expression for each thread context. Only rows where the value is true are displayed.

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