Threads

A thread is the basic unit of CPU utilization; it consists of a thread ID, a program counter, a register set, and a stack. A process can have one or more threads that execute concurrently. Threads within the same process share the same address space, code, data, and operating system resources. This shared nature makes communication and data exchange between threads much more efficient than between processes.

Thread Creation and Management

In Windows, threads are created using functions like CreateThread. This function returns a handle to the newly created thread, which can then be used to control its execution.

Threads can be created in various states: created, ready, running, suspended, and terminated. The operating system's scheduler is responsible for managing the execution of these threads, allocating CPU time, and switching between them.

Thread Synchronization

Because threads within a process share resources, it's crucial to manage access to these shared resources to prevent data corruption and race conditions. This is achieved through synchronization mechanisms. Windows provides several synchronization objects:

Synchronization Primitives

• Mutexes (Mutual Exclusion Objects): Allow only one thread to access a resource at a time.
• Semaphores: Control access to a resource that has a limited number of instances.
• Events: Allow threads to signal each other about the occurrence of an event.
• Critical Sections: Provide a lightweight mechanism for mutual exclusion within a single process.

Proper use of synchronization primitives is essential for writing robust and reliable multithreaded applications.

// Example of creating a thread (simplified)
HANDLE hThread = CreateThread(
    NULL,               // default security attributes
    0,                  // default stack size
    (LPTHREAD_START_ROUTINE)ThreadFunction, // thread function
    NULL,               // argument to thread function
    0,                  // default creation flags
    NULL);              // returns the thread identifier

if (hThread == NULL) {
    // Handle error
}
            

Thread Pools

For applications that frequently create and destroy threads, using thread pools can significantly improve performance by reducing the overhead associated with thread creation and termination. Thread pools maintain a set of worker threads that can execute tasks on demand.

Windows provides the Thread Pool API for managing thread pools efficiently. This allows your application to submit work items to the pool, and the pool will assign available threads to execute them.