Synchronization primitives

Synchronization primitives are essential tools for managing concurrent access to shared resources in multithreaded programming. There are several synchronization primitives, each with its own specific purpose and characteristics:

• Mutexes: Mutexes are used to enforce exclusive access to critical sections of code. A mutex can be locked by a thread, preventing other threads from entering the protected section until the mutex is unlocked. Mutexes guarantee that only one thread can execute the critical section at any given time, ensuring data integrity and preventing race conditions.
• Semaphores: Semaphores are more versatile than mutexes and can be used for a wider range of synchronization tasks, including signaling between threads. A semaphore maintains an integer counter that can be incremented (signaling) or decremented (waiting) by threads. Semaphores allow for more complex coordination patterns, such as counting semaphores (for resource allocation) and binary semaphores (similar to mutexes).
• Condition variables: Condition variables are used for thread synchronization based on specific conditions. Threads can block (wait on) a condition variable until a particular condition becomes true. Other threads can signal the condition variable, causing waiting threads to wake up and continue execution. Condition variables are often used in conjunction with mutexes to achieve more fine-grained synchronization and avoid busy waiting.
• Additional synchronization primitives: In addition to the core synchronization primitives discussed previously, there are several other synchronization mechanisms:
  • Barriers: Barriers allow a group of threads to synchronize their execution, ensuring that all threads reach a certain point before proceeding further
  • Read-write locks: Read-write locks provide a way to control concurrent access to shared data, allowing multiple readers but only a single writer at a time
  • Spinlocks: Spinlocks are a type of mutex that involves busy waiting, continuously checking a memory location until it becomes available

In Chapters 4 and 5, we will see the synchronization primitives implemented in the C++ Standard Template Library (STL) in depth and examples of how to use them.

Choosing the right synchronization primitive

The choice of the appropriate synchronization primitive depends on the specific requirements of the application and the nature of the shared resources being accessed. Here are some general guidelines:

• Mutexes: Use mutexes when exclusive access to a critical section is required to ensure data integrity and prevent race conditions
• Semaphores: Use semaphores when more complex coordination patterns are needed, such as resource allocation or signaling between threads
• Condition variables: Use condition variables when threads need to wait for a specific condition to become true before proceeding

Effective use of synchronization primitives is crucial for developing safe and efficient multithreaded programs. By understanding the purpose and characteristics of different synchronization mechanisms, developers can choose the most suitable primitives for their specific needs and achieve reliable and predictable concurrent execution.