Go是否会阻塞诸如Node之类的处理器密集型操作？

Question

Go is great for concurrency, tasks are passed as go-routines, and go-routines are processed in a virtual processor, whenever one go-routine experience a blocking operation (a database call), the go-routine is moved to another virtual processor on a different thread, which is most of the time run on another physical processor ... now, we achieve parallelism.

Node.js has a similar technique (except everything happens on the same thread), but putting all waiting virtual processes in a waiting queue, till they receive responses from the blocking resource (DB, URL), then they are send to be processed.

The down side of Node.js, is its inability to handle processor intensive operations (for loop is an example), and the virtual process being in action, will take all the time till finish without preemption, that's why Node.js is regarded wisely before it's used in critical systems, despite it's high concurrency availability.

Yes, Go spawns a new thread to handle the blocking go-routine, but how about the processor intensive operations, are they regarded the same, or suffer from Node problems?

Answer 1

Yes, but it's much more difficult to run into in practice than with Node, and much easier to recover from. Node is single-threaded unless you write explicitly multiprocess code (which isn't always easy, especially if you want to be portable). Go uses N:M scheduling with a certain maximum number of running threads (equal to the number of logical CPUs by default, but tunable). Note running: a goroutine that is waiting for a blocking operation is "frozen" and doesn't count as occupying a running thread.

So, if you have a single goroutine doing something CPU-intensive, it generally won't have an impact on other goroutines' ability to run, because there are a bunch of other threads available to run them. If all of your goroutines are occupied with computation, then it's true that other ones won't get a chance to run until one gives up the CPU. This might not necessarily be a problem if they're actually getting work done, since all of your CPUs are doing actual work, but of course sometimes it can be in latency-sensitive situations.

If it is a problem, three solutions come to mind:

1. Use runtime.Gosched during long computations to yield control of the processor, allowing other goroutines a chance to run. No other change has to be made; it's just a way of working with the cooperative scheduler. Gosched might return immediately, or it might return later.

2. Use a worker pool to limit the amount of parallel CPU-intensive work to less than GOMAXPROCS. Go makes this pretty easy.

3. Flipside of the same coin: raise GOMAXPROCS above the expected number of parallel compute tasks. This is probably the worst of the ideas, and will hurt scheduling at least somewhat, but it will still work, and ensure you have threads available for handling events.