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I am confused by goroutine, user thread, and kernel thread concepts
From effective go introduce goroutine, so what does os threads means which mentioned by the paper? Does it mean user thread or kernel thread?
From go-scheduler paper, I learn about M G P, and why the numbers of P is equal to the numbers of CPU? If all the cpus serve for the go program, but other program in the os system have no cpu thread to execute?
How many kernel thread generated by the os system?
500
There is one-to-one relationship of user-level thread to the kernel-level thread. This model provides more concurrency than the many-to-one model. It also allows another thread to run when a thread makes a blocking system call. It supports multiple threads to execute in parallel on microprocessors.
Threads are hardware dependent. Goroutines have easy communication medium known as channel. Thread does not have easy communication medium. Due to the presence of channel one goroutine can communicate with other goroutine with low latency.
A goroutine is a lightweight execution thread in the Go programming language and a function that executes concurrently with the rest of the program. Goroutines are incredibly cheap when compared to traditional threads as the overhead of creating a goroutine is very low.
There exist a strong a relationship between user level threads and kernel level threads. Dependencies between ULT and KLT : Use of Thread Library : Thread library acts as an interface for the application developer to create number of threads (according to the number of subtasks) and to manage those threads.
Let's include the picture from the go-scheduler page you linked to.
And establish the terminology:
goroutines are what we are most familiar with in Go, and could be considered user threads. A more technical name for those is Green Threads.
P is used to perform the mapping from many goroutines to many OS threads. There is one per OS thread, and the number is determined by the value of GOMAXPROCS (by default, the number of CPUs as reported by your system).
So, to answer your questions in order:
GOMAXPROCS defaults to the number of cores, but you can change that. Just because you can run on all cores does not mean you're not leaving CPU time for other processes. Concurrency usually involves a lot of waiting for IO. Even if you're going crazy hashing things, the kernel scheduler will boot you off to run other things.ps -eL, my system currently has 1434, some of them actual kernel jobs, some for my go program.You can find a really good explanation of OS vs Green threads in this answer
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