Managing Threading Errors with Intel? Parallel Inspector XE

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Copyright ? 2010, Intel Corporation. All Rights Reserved.Table of Contents

Disclaimer    ii

Parallelism Tools – Checking for Thread Correctness    1

Activity 1 - Choose, Build and Run a project    1

Activity 2 - Configure and Run Analysis    9

Activity 3 - Manage result data after analysis    13

Activity 4 - Resolve, Rebuild and Rerun    21

Parallelism Tools – Checking for Thread Correctness    

Activity 1 – Choose, Build and Run a Project

The application is a 2-D ray tracer/renderer called tachyon written in C++. The code is small enough that you may be able to identify potential memory access violations by visual inspection. If you identify and make a list of problems, check your list with the list that Parallel Inspector XE identifies.

Choose a project

1. With Windows Explorer*, locate the samples folder in the Parallel Inspector XE directory.
2. From the Microsoft Visual Studio* menu, choose File > Open > Project/Solution.
3. In the Open Project dialog box, open the filesamples\windows\tachyon_insp_xe\vc8\tachyon_insp_xe.sln fileby double-clicking it.

   This should now display tachyon_insp_xe solution in the Solution Explorer.

1. In the Solution Explorer, right-click the find_and_fix_threading_errors project and choose Set as Startup Project from among the menu options.

Build a project    

1. We first need to verify debug mode is configured to produce the best results. So in the Solution Explorer, right-click the find_and_fix_threading_errors project and choose Properties to display the Property Pages dialog box.
2. Verify the Configuration drop-down list is set to Debug or Active(Debug).

   

1. In the left pane, choose Configuration Properties > C/C++ > General.
2. Verify the Debug Information Format is set to Program Database (/Zi) or Program Database for Edit & Continue (/ZI).

   

3. In the left pane, choose Configuration Properties > C/C++ > Optimization.
4. Verify the Optimization field is set to Disabled (/Od).

   

5. In the left pane, choose Configuration Properties > C/C++ > Code Generation.
6. Verify the Runtime Library field is set to Multi-threaded DLL (/MD) or Multi-threaded Debug DLL (/MDd).

   

7. In the left pane, choose Configuration Properties > Linker > Debugging.
8. Verify the Generate Debug Info field is set to Yes (/DEBUG).

   

9. Verify the project is set to build in debug mode. Click the Configuration Manager button and verify the Active solution configuration drop-down list is set to Debug.

   

10. Click the Close button to close the Configuration Manager dialog box.
11. Click the OK button to close the Property Pages dialog box.

Run a project

1. From the Visual Studio* menu, choose Debug > Start Without Debugging.
2. When the Visual Studio* IDE responds this project is out of date, click Yes to build the project.
3. The application is run but the application output window will be empty and grey because of memory errors in the code!
4. You verified the find_and_fix_threading_errors project is set to produce the most accurate, complete results, compiled and linked the project and ensured the resulting find_and_fix_threading_errors.exe file runs on your system outside the Inspector XE.

    

Activity 2 – Configure and Run analysis

Configure a threading error analysis

1. From the Visual Studio* menu, choose Tools > Intel Inspector XE 2011 > New Analysis to display an Analysis Type window similar to the following:

   

2. Open the Threading Error Analysis folder and choose the Detect Deadlocks and Data Races analysis type to display a window similar to the following. (If necessary, click the icon in the Details region to display analysis type characteristics.)

   

1. After you finish experimenting, ensure your Analysis Type window resembles the following window:

   

2. You chose a preset analysis type of intermediate scope to detect memory errors in the find_and_fix_memory_errors.exe file.

Run a threading error analysis

1. Click the Analyze button on the Analysis Type window to:

• Execute the find_and_fix_threading_errors.exe file.
• Identify memory errors that may need handling.
• Collect the result in a folder in the tachyon_insp_xe\vc8\My Inspector XE 2011 Project - find_and_fix_threading_errors folder.
• Finalize the result (convert symbol information into filenames and line numbers, perform duplicate elimination, and form problem sets).

1. During collection, the Inspector XE displays a Collection Log window similar to the following:

    

Activity 3 – Manage result data after analysis

After analysis (both collection and finalization) completes successfully, the Inspector XE displays the Summary window:

Choose Problem Set

Start exploring a threading error.

    Interpret the Summary window

Choose a problem set

Click the data row for the Data race problem set in the find_and_fix_threading_errors.cpp source file to display a window similar to the following:

This Data race problem set contains one or more problems composed of Read and Write observations.

Choose a focus observation

Double-click the data row for the X2 Write observation to display the Sources window, which provides more visibility into the error:

Interpret Result Data

In this section, we will see how to determine the cause of the detected threading error.

To interpret the Sources window:

To interpret window icons:

To view source code for another observation:

Double click the data row for the X4 Read observation in the Observations in Problem Set pane to display a window similar to the following:

Notice the window changes:

• The Related Observation Code pane now shows the source code for the X4 Read observation.
• The icon for the X4 Read observation is now instead of in the Observations in Problem Set pane (and throughout the Sources window).

Understand the issue:

A Write -> Write Data race problem occurs when multiple threads write to the same memory location without proper synchronization. A Write -> Read Data race problem occurs when one thread writes to, while a different thread concurrently reads from, the same memory location.

The commenting in the Focus Observation Code window identifies the cause of the Data race problems: Multiple threads are concurrently accessing the global variable col. One possible correction strategy: change the global variable to a local variable.

Access more information on interpreting and resolving problems:

1. Right-click any observation in the Observations in Problem Set pane.
2. Choose Explain Problem to display Inspector XE Help information for the Data race problem type.

Activity 4 – Resolve, Rebuild and Rerun

Resolve an issue:

1. Scroll to this source code near line 80 in the Focus Observation Code pane: color col;
2. Double-click the line to open the find_and_fix_threading_errors.cpp source file in a separate tab where you can edit it with the Visual Studio* editor:

1. Comment color col; and uncomment //color col; near line 89:

1. Click the r000ti2 tab to redisplay the Sources window:

Rebuild and Rerun Analysis

To see if your edits resolved the memory errors:

• Rebuild the project with your edited source code.
• Run another analysis.
• Start managing result data after collection.

To rebuild the project:

1. Right-click the find_and_fix_threading_errors project in the Solution Explorer.
2. Choose Build.

To run another analysis:

From the Visual Studio* menu, choose Tools > Intel Inspector XE 2011 > Analyze As... > Threading Error Analysis / Detect Deadlocks and Data Races to run another analysis of the same analysis type:

Notice the image now displays.

To start managing result data after collection:

After analysis (both collection and finalization) completes successfully, the Inspector XE displays the Summary window:

Notice the Inspector XE:

• Created a new result tab.
• No longer detects problems in the find_and_fix_threading_errors.cpp file