Hi GHC devs,

I want to measure the CPU time spent in a particular Haskell thread across thread yield points. I am assuming Haskell threads do not keep track of per thread cpu time. Therefore, to measure it I have to use the thread cpu clock (CLOCK_THREAD_CPUTIME_ID) provided by the OS (Linux). But Haskell threads can keep jumping across multiple OS threads so the OS thread's CPU time cannot be used reliably.

To solve that issue I thought I could use bound threads. From the documentation it sounded like bound threads are exclusively bound to a particular OS thread so we can get thread cpu time from the OS and use it.

However, if I print the thread id for a bound thread using "gettid" (OS thread id on Linux) or using "pthread_self" (pthread id), both these thread ids are changing for the same Haskell thread which is a bound thread. Is that expected, or am I doing something wrong?

My questions:

* Are bound threads really bound to a particular OS thread or they can use multiple OS threads for executing Haskell code, and only use a fixed OS thread for FFI code?

* Is there a way to make this work? Can we obtain the thread cpu time reliably across thread yield points? Is there a way to really bind Haskell threads to OS threads?

* Is there a better or alternative way to get the thread CPU time?

Thanks,

Harendra