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
   8 // Linux futex.
   9 //
  10 //      futexsleep(uint32 *addr, uint32 val)
  11 //      futexwakeup(uint32 *addr)
  12 //
  13 // Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
  14 // Futexwakeup wakes up threads sleeping on addr.
  15 // Futexsleep is allowed to wake up spuriously.
  16
  17 #include <errno.h>
  18 #include <string.h>
  19 #include <time.h>
  20 #include <sys/types.h>
  21 #include <sys/stat.h>
  22 #include <fcntl.h>
  23 #include <unistd.h>
  24 #include <syscall.h>
  25 #include <linux/futex.h>
  26
  27 typedef struct timespec Timespec;
  28
  29 // Atomically,
  30 //      if(*addr == val) sleep
  31 // Might be woken up spuriously; that's allowed.
  32 // Don't sleep longer than ns; ns < 0 means forever.
  33 void
  34 runtime_futexsleep(uint32 *addr, uint32 val, int64 ns)
  35 {
  36         Timespec ts, *tsp;
  37
  38         if(ns < 0)
  39                 tsp = nil;
  40         else {
  41                 ts.tv_sec = ns/1000000000LL;
  42                 ts.tv_nsec = ns%1000000000LL;
  43                 // Avoid overflow
  44                 if(ts.tv_sec > 1<<30)
  45                         ts.tv_sec = 1<<30;
  46                 tsp = &ts;
  47         }
  48
  49         // Some Linux kernels have a bug where futex of
  50         // FUTEX_WAIT returns an internal error code
  51         // as an errno.  Libpthread ignores the return value
  52         // here, and so can we: as it says a few lines up,
  53         // spurious wakeups are allowed.
  54         syscall(__NR_futex, addr, FUTEX_WAIT, val, tsp, nil, 0);
  55 }
  56
  57 // If any procs are sleeping on addr, wake up at most cnt.
  58 void
  59 runtime_futexwakeup(uint32 *addr, uint32 cnt)
  60 {
  61         int64 ret;
  62
  63         ret = syscall(__NR_futex, addr, FUTEX_WAKE, cnt, nil, nil, 0);
  64
  65         if(ret >= 0)
  66                 return;
  67
  68         // I don't know that futex wakeup can return
  69         // EAGAIN or EINTR, but if it does, it would be
  70         // safe to loop and call futex again.
  71         runtime_printf("futexwakeup addr=%p returned %D\n", addr, ret);
  72         *(int32*)0x1006 = 0x1006;
  73 }
  74
  75 void
  76 runtime_osinit(void)
  77 {
  78         runtime_ncpu = getproccount();
  79 }
  80
  81 void
  82 runtime_goenvs(void)
  83 {
  84         runtime_goenvs_unix();
  85 }