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 %lld\n", addr, (long long)ret);
  72         *(int32*)0x1006 = 0x1006;
  73 }
  74
  75 #ifndef O_CLOEXEC
  76 #define O_CLOEXEC 0
  77 #endif
  78
  79 static int32
  80 getproccount(void)
  81 {
  82         int32 fd, rd, cnt, cpustrlen;
  83         const char *cpustr;
  84         const byte *pos;
  85         byte *bufpos;
  86         byte buf[256];
  87
  88         fd = open("/proc/stat", O_RDONLY|O_CLOEXEC, 0);
  89         if(fd == -1)
  90                 return 1;
  91         cnt = 0;
  92         bufpos = buf;
  93         cpustr = "\ncpu";
  94         cpustrlen = strlen(cpustr);
  95         for(;;) {
  96                 rd = read(fd, bufpos, sizeof(buf)-cpustrlen);
  97                 if(rd == -1)
  98                         break;
  99                 bufpos[rd] = 0;
 100                 for(pos=buf; (pos=(const byte*)strstr((const char*)pos, cpustr)) != nil; cnt++, pos++) {
 101                 }
 102                 if(rd < cpustrlen)
 103                         break;
 104                 memmove(buf, bufpos+rd-cpustrlen+1, cpustrlen-1);
 105                 bufpos = buf+cpustrlen-1;
 106         }
 107         close(fd);
 108         return cnt ? cnt : 1;
 109 }
 110
 111 void
 112 runtime_osinit(void)
 113 {
 114         runtime_ncpu = getproccount();
 115 }
 116
 117 void
 118 runtime_goenvs(void)
 119 {
 120         runtime_goenvs_unix();
 121 }