{"id":5435,"date":"2018-05-04T05:30:38","date_gmt":"2018-05-04T05:30:38","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/c-core-guidelines-use-tools-to-validate-your-concurrent-code\/"},"modified":"2023-06-26T11:51:26","modified_gmt":"2023-06-26T11:51:26","slug":"c-core-guidelines-use-tools-to-validate-your-concurrent-code","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/c-core-guidelines-use-tools-to-validate-your-concurrent-code\/","title":{"rendered":"C++ Core Guidelines: Use Tools to Validate your Concurrent Code"},"content":{"rendered":"

Today, I’m happy to write about the probably most important C++ Core Guidelines for concurrency rule: Whenever feasible, use tools to validate your concurrent code. Not all, but many bugs can be detected with tools, and each fixed bug is a good bug. Here are two tools that gave me precious help in the last few years: ThreadSanitizer<\/a> and CppMem<\/a>.<\/p>\n

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 <\/p>\n

 \"wrench<\/p>\n

Here is the rule for today:<\/p>\n

CP.9: Whenever feasible use tools to validate your concurrent code<\/a><\/h2>\n

This post is based on personal experience. On the one hand, a lot of my students in my multithreading classes wrote programs with data race; on the other hand, I implemented a lot of multithreading programs with bugs. How can I be sure? Because of the dynamic code analysis tool ThreadSanitizer<\/a> and the static code analysis tool CppMem<\/a>. The use cases for ThreadSanitizer and CppMem are different.<\/p>\n

ThreadSanitizer gives you the big picture and detects if the execution of your program has a data race. CppMem gives you a detailed insight into small pieces of code, most of the time including atomics. You will get the answer to the question: Which interleavings are possible according to the memory model? <\/p>\n

Let’s start with ThreadSanitizer.<\/p>\n<\/p>\n

ThreadSanitizer<\/h3>\n

Here is the official introduction to ThreadSanitizer<\/a>: “ThreadSanitizer (aka TSan) is a data race detector for C\/C++. Data races are one of the most common and hardest-to-debug types of bugs in concurrent systems. A data race occurs when two threads access the same variable concurrently, and at least one access is written. C++11<\/a> standard officially bans data races as undefined behavior.”<\/p>\n

ThreadSanitizer is part of clang 3.2 and gcc 4.8; it supports Linux x86_64, and is tested on Ubuntu 12.04. You have to compile and link against -fsanitize=thread<\/span>, use at least optimization level -O2<\/span> and the flag -g<\/span> for producing debugging information: -fsanitize=thread -O2 -g<\/span>. <\/p>\n

The runtime overhead is significant:  the memory usage may increase by 5-10x and the execution time by 2-20x. But of course, you know the principal law of software development: First, your program should be correct than fast.<\/strong> <\/p>\n

The ping-pong game<\/h4>\n

Now, let’s see ThreadSanitizer in action. Here is a typical exercise I often have given in my multithreading classes to condition variables:<\/p>\n

Write a small ping pong game.<\/p>\n