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Threads vs. Async

Asked 2010-10-26T13:20:19.353
106

I have been reading up on the threaded model of programming versus the asynchronous model from this really good article. http://krondo.com/blog/?p=1209

However, the article mentions the following points.

  1. An async program will simply outperform a sync program by switching between tasks whenever there is a I/O.
  2. Threads are managed by the operating system.

I remember reading that threads are managed by the operating system by moving around TCBs between the Ready-Queue and the Waiting-Queue(amongst other queues). In this case, threads don't waste time on waiting either do they?

In light of the above mentioned, what are the advantages of async programs over threaded programs?

python multithreading asynchronous twisted
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First of all, note that a lot of the detail of how threads are implemented and scheduled are very OS-specific. In general, you shouldn't need to worry about threads waiting on each other, since the OS and the hardware will attempt to arrange for them to run efficiently, whether asynchronously on a single-processor system or in parallel on multi-processors.

Once a thread has finished waiting for something, say I/O, it can be thought of as runnable. Threads that are runnable will be scheduled for execution at some point soon. Whether this is implemented as a simple queue or something more sophisticated is, again, OS- and hardware-specific. You can think of the set of blocked threads as a set rather than as a strictly ordered queue.

Note that on a single-processor system, asynchronous programs as defined here are equivalent to threaded programs.

answered 2010-10-26T13:33:24.213

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