Compute (part 1)

0. Pitch

• demo: typical processes - from different executables - need for multi-process environment
• demo: video decoding with ffmpeg using libx264 - uses multithreading - parallel runs

1. Running an Application

• applications run as processes
• diagram: a process is a (virtual) address space and an execution context
• the execution context is called a thread - can be multiple - main thread + others
• demo: list all processes and list all threads in the system

2. Process Address Space

• process address space layout
• diagram: initializing / populating process address space (loading and initializing)
• diagram: roles of each zone

3. Process Thread(s)

• execution context: what do I need to run?
  • in summary, an IP and a stack pointer
  • a stack provides an execution flow (return path) and local context (local variables, function parameters)
• diagram: IP points to the same zone, SP to a different thread per stack
• threads share process address space
  • each thread has their own stack
• main thread
• demo: create a thread, see creation of a new stack
• demo: print IP and SP of each thread

4. Process Operations

• create process, kill process, wait process
  • from executable
• diagram: create process: create address space, load address space, create thread, start thread
• demo: posix_spawn()
• process hierarchy
• demo: waiting for a process
• zombie processes, orphan processes

5. Thread Operations

• create thread, wait for thread
  • from function
• demo: create and join

6. fork() and exec()

• diagram: fork() and exec() steps
• fork() only used for multiprocessing - alternative to multithreading
• demo: fork() + exec() vs posix_spawn()
• demo: strace for fork(), exec(), posix_spawn() and pthread_create()

Conclusion and Takeaways

• processes are the core component to run applications
• a process is an address space and one or more threads (execution contexts)
• threads share process address space (except for the stack)
• processes form a hierarchy, a process is created by another process
• processes wait for child processes