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There are some situations where applications need to execute lots of asynchronous concurrent operations. OS-level threads could be used for this purpose, but an application can create only a limited count of threads. As for CPU utilization there is no significant performance gain if more threads are created than physical cores available on a CPU. In fact threads could be used for parallel processing on a multi-core CPU and for writing more readable code. OS-level threads should be mainly used for parallelism and better CPU utilization. If a programmer needs to write code which will be called asynchronously, then OS-level threads will be rather expensive in perspective of system resources.

CPU context switching methods

  • Cooperative (use of explicit Yield call)
  • Preemptive (periodic timer based)
  • Combined


  • Unlimited number of instances (limited by available memory)
  • Fast switching, creation, destruction
  • Automatic thread pool management by physical CPU core count
  • Ability to run in main loop only (without TThread instances)
  • Provide own synchronization tools (Yield, Sleep, CriticalSection, Semaphore, Mutex, WaitForMultipleObjects, Queues, Synchronize, ...)
  • Priority control
  • Support for view list of all microthreads


  • MicroThreading - Lazarus package, functional yet not finished, not multi-platform, needs patching the Free Pascal
  • STAX - Single Threaded Asynchronous EXecution framework (STAX for short) enables async/await style co-routines for Free Pascal

External links