Many Cores Java - Session One: Threads and Threads
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The document discusses threads and processes from hardware, software, and operating system perspectives, emphasizing the concept of multitasking on a single-core system. It distinguishes between cooperative and pre-emptive multitasking, explaining the impact of context switching, caches, and performance considerations. The author also encourages practical exercises and measurements on both Windows and Linux environments.
Many Cores Java - Session One: Threads and Threads
- 1. Threads and Threads session one starting with a single core copyright 2013 Robert Burrell Donkin robertburrelldonkin.name this work is licensed under a Creative Commons Attribution 3.0 Unported License
- 2. Threads, Threads and Processes from the ● hardware perspective ○ a thread is a serial code sequence ● software perspective ○ a thread abstracts a serial code sequence ● operating system perspective ○ a process abstracts an application instance
- 3. Multi-tasking a Single Core ● on a single core ○ a multitasking operating system ■ uses scheduling ■ to create the illusion of parallelism ● a software platform may also ○ use scheduling to create the illusion of parallelism ○ but then this is more often called multi-threading
- 4. Approaches to Multi-Tasking ● cooperative (or voluntary) multi-tasking ○ time-sharing ○ background processing ○ early Apple PCs ○ now rarely used ● pre-emptive multi-tasking ○ time-slicing ○ Windows 95 PCs ○ now almost universal
- 5. Why Multi-Task...? ● liveliness ● responsiveness ○ (to people) ● performance ○ (sometimes)
- 6. Context Switch ● a context switch ○ stores the current execute state, and ○ restores an execution state from storage ● from a CPU perspective ○ this is an expensive operation ● but is often cheap in comparison
- 7. Caches, Caches, Caches ● Moore's Law ○ the number of transistors doubles every 2 years ● but ○ diminishing returns from longer pipelines ○ popularity of multi-tasking ● so more and bigger caches ● so context switching cost now usually low ● but scales in a non-linear fashion ● excessive context switching expensive
- 8. Pre-emptive multi-tasking operating systems use involuntary context switching to provide the illusion of parallel processes even when the hardware supports only a single thread of execution. Take Away
- 9. Break Out ● Exercises ○ https://github.com/RobertBurrellDonkin/kata-manycore- threadsandthreads ● Try ○ On Windows ■ perfmon ■ typeperf ○ On Linux ■ vmstat ■ iostat ■ mpstat