Threads
Threads are the basic units to which a process can allocate CPU time. A thread can execute any part of the process's code, including code within another thread. Multiple threads can exist within the same process and share its resources, such as memory, open files, and other resources. This allows for concurrent execution of tasks within an application.
Thread Objects
A thread object provides a handle to the thread and contains information about its state, priority, and execution context. You can use thread objects to manage thread behavior, control thread priorities, and synchronize thread execution.
Key Thread Functions
The Windows API provides a rich set of functions for managing threads:
| Function | Description |
|---|---|
CreateThread |
Creates a new thread to execute within the virtual address space of the calling process. |
ExitThread |
Terminates the calling thread and closes its handle. |
GetThreadPriority |
Retrieves the priority level of the specified thread. |
SetThreadPriority |
Sets the priority class of the specified thread. |
SuspendThread |
Suspends the specified thread. Threads are suspended in a multithreaded process. |
ResumeThread |
Resumes the specified suspended thread. |
Sleep |
Suspends the current thread for a specified interval. |
WaitForSingleObject |
Waits until the specified object is in the signaled state or the time-out interval elapses. |
Thread States
A thread can be in one of the following states:
- Running: The thread is currently executing code on the CPU.
- Ready: The thread is ready to run but is waiting for the scheduler to allocate CPU time.
- Suspended: The thread has been suspended by another thread or by a system call and cannot execute until it is resumed.
- Terminated: The thread has finished execution.
Thread Synchronization
When multiple threads access shared resources, synchronization mechanisms are necessary to prevent data corruption and ensure predictable behavior. Common synchronization primitives include:
- Mutexes: Mutual exclusion objects that allow only one thread to access a resource at a time.
- Semaphores: Allow a specified number of threads to access a resource concurrently.
- 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.
CreateMutex or InitializeCriticalSection are often preferred for their performance characteristics.
Thread Pools
Thread pools manage a collection of worker threads that can be used to execute callbacks. This can be more efficient than creating and destroying threads on demand, especially for short-lived tasks.
Key functions related to thread pools include:
CreateThreadpoolSetThreadpoolThreadMaximumSetThreadpoolThreadMinimumPostThreadpoolWork