Managing Memory 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 Memory Access Violations    1

Activity 1 - Choose, Build and Run a project    1

Activity 2 - Configure and Run Analysis    8

Activity 3 - Manage result data after analysis    12

Activity 4 - Resolve, Rebuild and Rerun    17

Parallelism Tools – Checking for Memory Access violations    

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_memory_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_memory_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_memory_errors project is set to produce the most accurate, complete results, compiled and linked the project and ensured the resulting find_and_fix_memory_errors.exe file runs on your system outside the Inspector XE.

    

Activity 2 – Configure and Run analysis

Configure a memory 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 Memory Error Analysis folder and choose the Detect Memory Problems 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 memory error analysis

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

• Execute the find_and_fix_memory_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_memory_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 memory error.

    Interpret the Summary window

Choose a problem set

Double-click the data row for the Mismatched allocation/deallocation problem set source file 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 memory error.

To interpret the Sources window:

To interpret window icons:

To understand the issue:

Look at the code in the Focus Observation Code pane and the Related Observation Code pane.

The code in the Allocation site observation in the Related Observation Code pane contains a new allocator, while the code in the Mismatched deallocation site observation in the Focus Observation Code pane contains a free() deallocator.

A Mismatched allocation/deallocation problem occurs when you attempt a deallocation with a function that is not the logical reflection of the allocator. In the C++ programming language, the following are matched reflections:

• newanddelete
• new[]anddelete[]
• malloc()andfree()

Only the matching deallocation technique is uniquely aware of all the memory allocation techniques and internal data storage used by the allocation technique. Using the wrong deallocation technique will almost certainly corrupt memory reclamation, its sole job.

Activity 4 – Resolve, Rebuild and Rerun

Resolve an issue:

1. Double-click the highlighted code in the Focus Observation Code pane to open the find_and_fix_memory_errors.cpp source file in a separate tab where you can edit it with the Visual Studio* editor:

1. Comment free(drawing);and uncomment//delete drawing;:

1. Click the r000mi2 tab to redisplay the Sources window:

1. Click the Summary button to redisplay the Summary window:

Resolve another issue:

Now resolve another detected memory error by following the below steps:

Chooseanother problem set:

In the Problem Sets pane on the Summary window, double-click the data row for a Memory Leak problem set to display the Sources window:

To access more information on interpreting and resolving problems:

1. Right-click the Allocation site observation in the Observations in Problem Set pane.
2. Choose Explain Problem to display Inspector XE Help information for the Memory Leak problem type.

    

To interpret result data:

A Memory leak problem occurs when a block of memory is allocated and never released.

The Allocation site observation represents the location from which the memory block was allocated. Here, the source code shows a malloc() allocator.

Scroll the source code to near line 180:

The issue is obvious: The free() call that releases the memory allocated by the malloc() call is commented out.

To resolve memory leak problems (while avoiding related mismatched allocation/deallocation problems): Match anymalloc()call with afree()call, anewwith adelete, and anew[]with adelete[]as soon as all use of the allocated space has occurred, but not sooner. Never mix and match.

Be aware:

• If you do not deallocate soon enough, you waste space the program might need.
• If you deallocate too soon, you may do one of the following:
  • Corrupt your memory allocator or the space it manages when you later write to that space.
  • End up with bogus data if you later read that space when you previously returned it to the memory allocator.
• Make sure you free any space allocated within a function prior to exiting that function, or else make sure the function caller does the deallocation for the called function.

To resolve the issue:

1. Click the find_and_fix_memory_errors.cpp tab to redisplay the find_and_fix_memory_errors.cpp source file in the Visual Studio* editor:

1. Uncomment//free(local_mbox);:

1. Click the r000mi2 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_memory_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... > Memory Error Analysis / Detect Memory Problems 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 detected Mismatched allocation/deallocation and Memory leak problems.

Try fixing the remaining problem set(s) yourself.