GPU621/Sentinel

Multithreaded Application Debugging in Visual Studio

• The project is based on the material outlined in "Debug multithreaded applications in Visual Studio" section of MSDN documentation and other related MSDN documentation.

Group Members

1. Ekaterina Zaytseva
2. Mohammad Yasir
3. Natan Ross
4. eMail All

Introduction

Multithreaded applications debugging overview

Debugging is one of the crucial software development stages. While all of us know the importance and the basics of debugging in the Visual Studio, debugging the multithreaded applications is more complicated than that of the serial programs we were used to before. The first problem of the multithreaded debugging is keeping track of multiple threads instead of just one as we did with the serial programs. Secondly, having multiple threads introduces new kinds of bugs and issues that can seriously affect the output of the software. Such issues include race conditions and deadlocks. A race condition is the behavior of the system when the output is dependent on the sequence of other events or commands. It becomes a bug when the events are out of order (Race condition wiki). Deadlock is a situation when each member of the group (a group of threads in our case) is waiting for some other member to take action, it typically happens when mutual exclusion is executed incorrectly, and the lock on the resource cannot be released (Deadlock wiki).

Visual Studio tools for multithreaded debugging

Threads Window

Parallel Stacks Window

Parallel Watch Window

Debug Location Windows

Tasks Windows

GPU Threads Windows

Attach to Process Dialog

Processes Window

Visual Studio provides the developers with a variety of tools to assist with the multithreaded application debugging:

1. Threads window - Allows to view and manipulate the threads, also provides partial call stack for each of the threads

2. Thread markers - Icon resembling two cloth threads indicating where a thread is stopped. Provides a DataTip containing the name and thread ID, as well as thread manipulation shortcut menu

3. Parallel Stacks window - Shows call stack information for all the threads in the program

4. Parallel Watch window - Tracks the values produced by the multithreaded expression

5. Debug Location toolbar - Allows manipulating threads and processes

6. Tasks window - Lists all the current parallel and scheduled tasks

7. GPU Threads window - Allows working with the GPU threads

8. Attach to Process dialog box - Allows the developer to attach the VS debugger to the process, enables the process debugging

9. Processes window - Lists all the processes currently attached to the debugger

The tools mentioned above can be divided into the following categories depending on the multithreading technique:

1. Threads - Threads windows, Thread markers, Parallel Stacks window, Parallel Parallel Watch window, Debug Location toolbar

2. Tasks - Parallel Stacks window, Parallel Watch window, Tasks window

3. GPU Threads - GPU Threads window

4. Processes - Attach to Process dialog, Processes window, Debug Location toolbar

For our project, we are going to do OpenMP debugging, so we will need the following tools:

• Breakpoints
• Watch window
• Thread markers
• Threads window
• Parallel Watch window
• Parallel Stacks window

Basic Debugging Steps

1. Setting up a Solution in Visual Studio 2017 Comunity Edition
2. Build in Debug mode
3. Double-check the outputs
4. Start where the bug is

Setting up a Solution in Visual Studio 2017 Comunity Edition

This tutorial begins after the installation and setup of Intel Parallel Studios. Also, you should already have openMP running properly on your setup.

1. Create a new project and select the properties.

2. Click the configuration manager at the top right of your properties window.

3. Create a new configuration

4. Copy your current working openMP configuration for the current project (with the working openMP solution) and give the new configuration a nice name

.

5. Go to the C/C++ configuration and then select optimization. Ensure that optimization is turned off for debugging.

6. Finally, ensure that all threads stop when hitting a breakpoint by editing the debug configuration and enabling the setting Break all processes when one process breaks.

How to Debug Multithreaded Application in VS

Tools

When working with the debugger in VS to debug a multi-threaded application, the two most important windows are: Local variables window (on the left), and the Parallel Watch window (on the right):

1. Walkthrough (workshop-style)

Note: Add the link to the configurations