libgo/runtime/time.goc

   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 // Time-related runtime and pieces of package time.
   6
   7 package time
   8
   9 #include "runtime.h"
  10 #include "defs.h"
  11 #include "arch.h"
  12 #include "malloc.h"
  13
  14 static Timers timers;
  15 static void addtimer(Timer*);
  16 static bool deltimer(Timer*);
  17
  18 // Package time APIs.
  19 // Godoc uses the comments in package time, not these.
  20
  21 // time.now is implemented in assembly.
  22
  23 // Sleep puts the current goroutine to sleep for at least ns nanoseconds.
  24 func Sleep(ns int64) {
  25         G *g;
  26
  27         g = runtime_g();
  28         g->status = Gwaiting;
  29         g->waitreason = "sleep";
  30         runtime_tsleep(ns);
  31 }
  32
  33 // startTimer adds t to the timer heap.
  34 func startTimer(t *Timer) {
  35         addtimer(t);
  36 }
  37
  38 // stopTimer removes t from the timer heap if it is there.
  39 // It returns true if t was removed, false if t wasn't even there.
  40 func stopTimer(t *Timer) (stopped bool) {
  41         stopped = deltimer(t);
  42 }
  43
  44 // C runtime.
  45
  46 static void timerproc(void*);
  47 static void siftup(int32);
  48 static void siftdown(int32);
  49
  50 // Ready the goroutine e.data.
  51 static void
  52 ready(int64 now, Eface e)
  53 {
  54         USED(now);
  55
  56         runtime_ready(e.__object);
  57 }
  58
  59 // Put the current goroutine to sleep for ns nanoseconds.
  60 // The caller must have set g->status and g->waitreason.
  61 void
  62 runtime_tsleep(int64 ns)
  63 {
  64         Timer t;
  65
  66         if(ns <= 0)
  67                 return;
  68
  69         t.when = runtime_nanotime() + ns;
  70         t.period = 0;
  71         t.f = ready;
  72         t.arg.__object = runtime_g();
  73         addtimer(&t);
  74         runtime_gosched();
  75 }
  76
  77 // Add a timer to the heap and start or kick the timer proc
  78 // if the new timer is earlier than any of the others.
  79 static void
  80 addtimer(Timer *t)
  81 {
  82         int32 n;
  83         Timer **nt;
  84
  85         runtime_lock(&timers);
  86         if(timers.len >= timers.cap) {
  87                 // Grow slice.
  88                 n = 16;
  89                 if(n <= timers.cap)
  90                         n = timers.cap*3 / 2;
  91                 nt = runtime_malloc(n*sizeof nt[0]);
  92                 runtime_memmove(nt, timers.t, timers.len*sizeof nt[0]);
  93                 runtime_free(timers.t);
  94                 timers.t = nt;
  95                 timers.cap = n;
  96         }
  97         t->i = timers.len++;
  98         timers.t[t->i] = t;
  99         siftup(t->i);
 100         if(t->i == 0) {
 101                 // siftup moved to top: new earliest deadline.
 102                 if(timers.sleeping) {
 103                         timers.sleeping = false;
 104                         runtime_notewakeup(&timers.waitnote);
 105                 }
 106                 if(timers.rescheduling) {
 107                         timers.rescheduling = false;
 108                         runtime_ready(timers.timerproc);
 109                 }
 110         }
 111         if(timers.timerproc == nil)
 112                 timers.timerproc = __go_go(timerproc, nil);
 113         runtime_unlock(&timers);
 114 }
 115
 116 // Delete timer t from the heap.
 117 // Do not need to update the timerproc:
 118 // if it wakes up early, no big deal.
 119 static bool
 120 deltimer(Timer *t)
 121 {
 122         int32 i;
 123
 124         runtime_lock(&timers);
 125
 126         // t may not be registered anymore and may have
 127         // a bogus i (typically 0, if generated by Go).
 128         // Verify it before proceeding.
 129         i = t->i;
 130         if(i < 0 || i >= timers.len || timers.t[i] != t) {
 131                 runtime_unlock(&timers);
 132                 return false;
 133         }
 134
 135         timers.len--;
 136         if(i == timers.len) {
 137                 timers.t[i] = nil;
 138         } else {
 139                 timers.t[i] = timers.t[timers.len];
 140                 timers.t[timers.len] = nil;
 141                 timers.t[i]->i = i;
 142                 siftup(i);
 143                 siftdown(i);
 144         }
 145         runtime_unlock(&timers);
 146         return true;
 147 }
 148
 149 // Timerproc runs the time-driven events.
 150 // It sleeps until the next event in the timers heap.
 151 // If addtimer inserts a new earlier event, addtimer
 152 // wakes timerproc early.
 153 static void
 154 timerproc(void* dummy __attribute__ ((unused)))
 155 {
 156         G *g;
 157         int64 delta, now;
 158         Timer *t;
 159         void (*f)(int64, Eface);
 160         Eface arg;
 161
 162         g = runtime_g();
 163         for(;;) {
 164                 runtime_lock(&timers);
 165                 now = runtime_nanotime();
 166                 for(;;) {
 167                         if(timers.len == 0) {
 168                                 delta = -1;
 169                                 break;
 170                         }
 171                         t = timers.t[0];
 172                         delta = t->when - now;
 173                         if(delta > 0)
 174                                 break;
 175                         if(t->period > 0) {
 176                                 // leave in heap but adjust next time to fire
 177                                 t->when += t->period * (1 + -delta/t->period);
 178                                 siftdown(0);
 179                         } else {
 180                                 // remove from heap
 181                                 timers.t[0] = timers.t[--timers.len];
 182                                 timers.t[0]->i = 0;
 183                                 siftdown(0);
 184                                 t->i = -1;  // mark as removed
 185                         }
 186                         f = t->f;
 187                         arg = t->arg;
 188                         runtime_unlock(&timers);
 189                         f(now, arg);
 190                         runtime_lock(&timers);
 191                 }
 192                 if(delta < 0) {
 193                         // No timers left - put goroutine to sleep.
 194                         timers.rescheduling = true;
 195                         g->status = Gwaiting;
 196                         g->waitreason = "timer goroutine (idle)";
 197                         runtime_unlock(&timers);
 198                         runtime_gosched();
 199                         continue;
 200                 }
 201                 // At least one timer pending.  Sleep until then.
 202                 timers.sleeping = true;
 203                 runtime_noteclear(&timers.waitnote);
 204                 runtime_unlock(&timers);
 205                 runtime_entersyscall();
 206                 runtime_notetsleep(&timers.waitnote, delta);
 207                 runtime_exitsyscall();
 208         }
 209 }
 210
 211 // heap maintenance algorithms.
 212
 213 static void
 214 siftup(int32 i)
 215 {
 216         int32 p;
 217         Timer **t, *tmp;
 218
 219         t = timers.t;
 220         while(i > 0) {
 221                 p = (i-1)/2;  // parent
 222                 if(t[i]->when >= t[p]->when)
 223                         break;
 224                 tmp = t[i];
 225                 t[i] = t[p];
 226                 t[p] = tmp;
 227                 t[i]->i = i;
 228                 t[p]->i = p;
 229                 i = p;
 230         }
 231 }
 232
 233 static void
 234 siftdown(int32 i)
 235 {
 236         int32 c, len;
 237         Timer **t, *tmp;
 238
 239         t = timers.t;
 240         len = timers.len;
 241         for(;;) {
 242                 c = i*2 + 1;  // left child
 243                 if(c >= len) {
 244                         break;
 245                 }
 246                 if(c+1 < len && t[c+1]->when < t[c]->when)
 247                         c++;
 248                 if(t[c]->when >= t[i]->when)
 249                         break;
 250                 tmp = t[i];
 251                 t[i] = t[c];
 252                 t[c] = tmp;
 253                 t[i]->i = i;
 254                 t[c]->i = c;
 255                 i = c;
 256         }
 257 }
 258
 259 void
 260 runtime_time_scan(void (*scan)(byte*, int64))
 261 {
 262         scan((byte*)&timers, sizeof timers);
 263 }