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The Go programming language
071d212a22
Fixes #1641. Actually it side steps the real issue, which is that the setitimer(2) implementation on OS X is not useful for profiling of multi-threaded programs. I filed the below using the Apple Bug Reporter. /* Filed as Apple Bug Report #9177434. This program creates a new pthread that loops, wasting cpu time. In the main pthread, it sleeps on a condition that will never come true. Before doing so it sets up an interval timer using ITIMER_PROF. The handler prints a message saying which thread it is running on. POSIX does not specify which thread should receive the signal, but in order to be useful in a user-mode self-profiler like pprof or gprof http://code.google.com/p/google-perftools http://www.delorie.com/gnu/docs/binutils/gprof_25.html it is important that the thread that receives the signal is the one whose execution caused the timer to expire. Linux and FreeBSD handle this by sending the signal to the process's queue but delivering it to the current thread if possible: http://lxr.linux.no/linux+v2.6.38/kernel/signal.c#L802 807 /* 808 * Now find a thread we can wake up to take the signal off the queue. 809 * 810 * If the main thread wants the signal, it gets first crack. 811 * Probably the least surprising to the average bear. 812 * / http://fxr.watson.org/fxr/source/kern/kern_sig.c?v=FREEBSD8;im=bigexcerpts#L1907 1914 /* 1915 * Check if current thread can handle the signal without 1916 * switching context to another thread. 1917 * / On those operating systems, this program prints: $ ./a.out signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread signal on cpu-chewing looper thread $ The OS X kernel does not have any such preference. Its get_signalthread does not prefer current_thread(), in contrast to the other two systems, so the signal gets delivered to the first thread in the list that is able to handle it, which ends up being the main thread in this experiment. http://fxr.watson.org/fxr/source/bsd/kern/kern_sig.c?v=xnu-1456.1.26;im=excerpts#L1666 $ ./a.out signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread signal on sleeping main thread $ The fix is to make get_signalthread use the same heuristic as Linux and FreeBSD, namely to use current_thread() if possible before scanning the process thread list. */ #include <sys/time.h> #include <sys/signal.h> #include <pthread.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> static void handler(int); static void* looper(void*); static pthread_t pmain, ploop; int main(void) { struct itimerval it; struct sigaction sa; pthread_cond_t cond; pthread_mutex_t mu; memset(&sa, 0, sizeof sa); sa.sa_handler = handler; sa.sa_flags = SA_RESTART; memset(&sa.sa_mask, 0xff, sizeof sa.sa_mask); sigaction(SIGPROF, &sa, 0); pmain = pthread_self(); pthread_create(&ploop, 0, looper, 0); memset(&it, 0, sizeof it); it.it_interval.tv_usec = 10000; it.it_value = it.it_interval; setitimer(ITIMER_PROF, &it, 0); pthread_mutex_init(&mu, 0); pthread_mutex_lock(&mu); pthread_cond_init(&cond, 0); for(;;) pthread_cond_wait(&cond, &mu); return 0; } static void handler(int sig) { static int nsig; pthread_t p; p = pthread_self(); if(p == pmain) printf("signal on sleeping main thread\n"); else if(p == ploop) printf("signal on cpu-chewing looper thread\n"); else printf("signal on %p\n", (void*)p); if(++nsig >= 10) exit(0); } static void* looper(void *v) { for(;;); } R=r CC=golang-dev https://golang.org/cl/4273113 |
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This is the source code repository for the Go programming language.
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--
Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set
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For example, if you extracted the tar file into $HOME/go, you might
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export GOROOT=$HOME/go
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See doc/install.html for more details.