Concurrency Models: Data Race Exclusion

• Excluded Variables
• Thread-Local Storage Operations
• Atomic Operations

Excluded Variables

Extension API prototype csonar_relay_ignore() is provided so that you can indicate to the CodeSonar analysis that one or more specific global or file-static variables are exempt from data race checking.

The shipped CodeSonar library models use this mechanism to exclude special variable errno from data race checks. Modern C compilers give each thread its own copy of errno.

Thread-Local Storage Operations

Data located in thread-local storage cannot be subject to data race problems, since only one thread is accessing the data.

Thread-Local Storage Set

CodeSonar ships with library models that allow it to recognize a number of operators and functions that set values in thread-local storage. Some examples are listed below.

Thread-Local Storage Get

CodeSonar ships with library models that allow it to recognize a number of operators and functions that get values in thread-local storage. Some examples are listed below.

Atomic Operations

When a particular block of code is guaranteed to be atomic (that is, to execute without interruption), memory reads and writes within that block will not participate in any data races and can be excluded from data race checks. CodeSonar models the following Win32 functions as atomic.

Creating New Models

If you are authoring a model, it is usually best to have the model call the already-modeled function that is most similar.

If no existing model is appropriate, write your model using the extension functions provided.

• To indicate that a global or file-static variable is exempt from data race checking, use csonar_relay_ignore().
• To indicate that a function writes to thread-local storage, use csonar_tls_set().
• To indicate that a function reads from thread-local storage, use csonar_tls_get().
• To indicate that a piece of code should be treated as executing atomically, model it as taking place while special lock &csonar_win32_atomic_lock is held.

  For example, suppose we have function myAtomicInc(), and want to make sure that CodeSonar treats it as executing atomically.

  int globalCounter;
  
  void myAtomicInc(){ globalCounter++; }
  

  Then our model inserts a csonar_mutex_acquire() statement at the beginning of the function body, and a csonar_mutex_release() statement at the end:

  int globalCounter;
  
  void myAtomicInc(){ 
      csonar_mutex_acquire(&csonar_win32_atomic_lock);
      globalCounter++; 
      csonar_mutex_release(&csonar_win32_atomic_lock);
  }