#16102: forkProcess causes weird GC summary in the child process -------------------------------------+------------------------------------- Reporter: osa1 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * cc: simonmar, bgamari (added) Comment: The problem is this: when we fork, in the child process CPU time starts from 0 (or at least from a lower value than the value in parent process), but we don't reset `start_init_cpu`, we use the value from the parent process. So `start_init_cpu` becomes larger than `getProcessCPUTime()` in the child process when it starts running. If we immediately then we can observe this state. Here's an example in gdb: (shortly after a `forkProcess()`, in child process): {{{
call getProcessCPUTime() $6 = 238056 print start_init_cpu $7 = 3994827 }}}
Not sure how to fix this, but some ideas: - Make the child process inherit the CPU time. (I'm not sure if this is possible though, or if it's possible in all platforms we want to support) - Reset all counters (start_init_cpu, gc times etc.) in the child process. Simon, Ben, any ideas on this? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16102#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler