libgo/runtime/thread-linux.c

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 #include "runtime.h"
   6 #include "defs.h"
   7 #include "signal_unix.h"
   8
   9 // Linux futex.
  10 //
  11 //      futexsleep(uint32 *addr, uint32 val)
  12 //      futexwakeup(uint32 *addr)
  13 //
  14 // Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
  15 // Futexwakeup wakes up threads sleeping on addr.
  16 // Futexsleep is allowed to wake up spuriously.
  17
  18 #include <errno.h>
  19 #include <string.h>
  20 #include <time.h>
  21 #include <sys/types.h>
  22 #include <sys/stat.h>
  23 #include <fcntl.h>
  24 #include <unistd.h>
  25 #include <syscall.h>
  26 #include <linux/futex.h>
  27
  28 typedef struct timespec Timespec;
  29
  30 // Atomically,
  31 //      if(*addr == val) sleep
  32 // Might be woken up spuriously; that's allowed.
  33 // Don't sleep longer than ns; ns < 0 means forever.
  34 void
  35 runtime_futexsleep(uint32 *addr, uint32 val, int64 ns)
  36 {
  37         Timespec ts;
  38         int32 nsec;
  39
  40         // Some Linux kernels have a bug where futex of
  41         // FUTEX_WAIT returns an internal error code
  42         // as an errno.  Libpthread ignores the return value
  43         // here, and so can we: as it says a few lines up,
  44         // spurious wakeups are allowed.
  45
  46         if(ns < 0) {
  47                 syscall(__NR_futex, addr, FUTEX_WAIT, val, nil, nil, 0);
  48                 return;
  49         }
  50         ts.tv_sec = runtime_timediv(ns, 1000000000LL, &nsec);
  51         ts.tv_nsec = nsec;
  52         syscall(__NR_futex, addr, FUTEX_WAIT, val, &ts, nil, 0);
  53 }
  54
  55 // If any procs are sleeping on addr, wake up at most cnt.
  56 void
  57 runtime_futexwakeup(uint32 *addr, uint32 cnt)
  58 {
  59         int64 ret;
  60
  61         ret = syscall(__NR_futex, addr, FUTEX_WAKE, cnt, nil, nil, 0);
  62
  63         if(ret >= 0)
  64                 return;
  65
  66         // I don't know that futex wakeup can return
  67         // EAGAIN or EINTR, but if it does, it would be
  68         // safe to loop and call futex again.
  69         runtime_printf("futexwakeup addr=%p returned %D\n", addr, ret);
  70         *(int32*)0x1006 = 0x1006;
  71 }
  72
  73 void
  74 runtime_osinit(void)
  75 {
  76         runtime_ncpu = getproccount();
  77 }
  78
  79 void
  80 runtime_goenvs(void)
  81 {
  82         runtime_goenvs_unix();
  83 }