Processes, Threads, and Scheduling
Processes hold a program's resources, threads execute its work, and the scheduler decides which runnable threads use CPU time. These ideas explain why concurrent programs can wait, contend, or respond at different speeds.
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Intro
Processes, Threads, and Scheduling
A program on disk is passive. A process is the operating system's running instance of that program. It holds resources such as an address space, open files, credentials, and one or more threads. A thread is an execution path within that process. It has execution state and can run instructions, block for work, or become runnable again.
This distinction gives you a useful starting point for concurrent systems. A process is usually a protection and ownership boundary. Threads inside it can coordinate through the same process resources, but that convenience creates shared-state risks. Separate processes need an explicit communication mechanism, but a failure in one process is more readily contained by its resource boundary.
What the scheduler does
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Sources
- https://pubs.opengroup.org/onlinepubs/9799919799/functions/V2_chap02.html
Supports
- POSIX process as an aggregation of system resources containing one or more schedulable threads
- Portable thread scheduling model, priorities, and scheduling policy concepts
- https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_mutex_lock.html
Supports
- Mutex lock behavior and mutual exclusion for protected shared state
- https://www.kernel.org/doc/html/latest/scheduler/
Supports
- Linux scheduler documentation index and scheduler-specific study path
- https://www.kernel.org/doc/html/latest/scheduler/sched-eevdf.html
Supports
- Fair allocation among runnable tasks and latency-sensitive selection in Linux EEVDF documentation
- https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html
Supports
- Runnable task selection, scheduler classes, regular batch and idle policies, and context-switching events
- https://cdn.kernel.org/doc/html/latest/scheduler/sched-deadline.html
Supports
- Linux deadline scheduling runtime, period, deadline, and timing-oriented workload model