libgo/runtime/sigqueue.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 // This file implements runtime support for signal handling.
   6 //
   7 // Most synchronization primitives are not available from
   8 // the signal handler (it cannot block, allocate memory, or use locks)
   9 // so the handler communicates with a processing goroutine
  10 // via struct sig, below.
  11 //
  12 // sigsend() is called by the signal handler to queue a new signal.
  13 // signal_recv() is called by the Go program to receive a newly queued signal.
  14 // Synchronization between sigsend() and signal_recv() is based on the sig.state
  15 // variable.  It can be in 3 states: 0, HASWAITER and HASSIGNAL.
  16 // HASWAITER means that signal_recv() is blocked on sig.Note and there are no
  17 // new pending signals.
  18 // HASSIGNAL means that sig.mask *may* contain new pending signals,
  19 // signal_recv() can't be blocked in this state.
  20 // 0 means that there are no new pending signals and signal_recv() is not blocked.
  21 // Transitions between states are done atomically with CAS.
  22 // When signal_recv() is unblocked, it resets sig.Note and rechecks sig.mask.
  23 // If several sigsend()'s and signal_recv() execute concurrently, it can lead to
  24 // unnecessary rechecks of sig.mask, but must not lead to missed signals
  25 // nor deadlocks.
  26
  27 package signal
  28 #include "config.h"
  29 #include "runtime.h"
  30 #include "arch.h"
  31 #include "malloc.h"
  32 #include "defs.h"
  33
  34 static struct {
  35         Note;
  36         uint32 mask[(NSIG+31)/32];
  37         uint32 wanted[(NSIG+31)/32];
  38         uint32 state;
  39         bool inuse;
  40 } sig;
  41
  42 enum {
  43         HASWAITER = 1,
  44         HASSIGNAL = 2,
  45 };
  46
  47 // Called from sighandler to send a signal back out of the signal handling thread.
  48 bool
  49 __go_sigsend(int32 s)
  50 {
  51         uint32 bit, mask, old, new;
  52
  53         if(!sig.inuse || s < 0 || (size_t)s >= 32*nelem(sig.wanted) || !(sig.wanted[s/32]&(1U<<(s&31))))
  54                 return false;
  55         bit = 1 << (s&31);
  56         for(;;) {
  57                 mask = sig.mask[s/32];
  58                 if(mask & bit)
  59                         break;          // signal already in queue
  60                 if(runtime_cas(&sig.mask[s/32], mask, mask|bit)) {
  61                         // Added to queue.
  62                         // Only send a wakeup if the receiver needs a kick.
  63                         for(;;) {
  64                                 old = runtime_atomicload(&sig.state);
  65                                 if(old == HASSIGNAL)
  66                                         break;
  67                                 if(old == HASWAITER)
  68                                         new = 0;
  69                                 else  // if(old == 0)
  70                                         new = HASSIGNAL;
  71                                 if(runtime_cas(&sig.state, old, new)) {
  72                                         if (old == HASWAITER)
  73                                                 runtime_notewakeup(&sig);
  74                                         break;
  75                                 }
  76                         }
  77                         break;
  78                 }
  79         }
  80         return true;
  81 }
  82
  83 // Called to receive the next queued signal.
  84 // Must only be called from a single goroutine at a time.
  85 func signal_recv() (m uint32) {
  86         static uint32 recv[nelem(sig.mask)];
  87         uint32 i, old, new;
  88
  89         for(;;) {
  90                 // Serve from local copy if there are bits left.
  91                 for(i=0; i<NSIG; i++) {
  92                         if(recv[i/32]&(1U<<(i&31))) {
  93                                 recv[i/32] ^= 1U<<(i&31);
  94                                 m = i;
  95                                 goto done;
  96                         }
  97                 }
  98
  99                 // Check and update sig.state.
 100                 for(;;) {
 101                         old = runtime_atomicload(&sig.state);
 102                         if(old == HASWAITER)
 103                                 runtime_throw("inconsistent state in signal_recv");
 104                         if(old == HASSIGNAL)
 105                                 new = 0;
 106                         else  // if(old == 0)
 107                                 new = HASWAITER;
 108                         if(runtime_cas(&sig.state, old, new)) {
 109                                 if (new == HASWAITER) {
 110                                         runtime_entersyscall();
 111                                         runtime_notesleep(&sig);
 112                                         runtime_exitsyscall();
 113                                         runtime_noteclear(&sig);
 114                                 }
 115                                 break;
 116                         }
 117                 }
 118
 119                 // Get a new local copy.
 120                 for(i=0; (size_t)i<nelem(sig.mask); i++) {
 121                         for(;;) {
 122                                 m = sig.mask[i];
 123                                 if(runtime_cas(&sig.mask[i], m, 0))
 124                                         break;
 125                         }
 126                         recv[i] = m;
 127                 }
 128         }
 129
 130 done:;
 131         // goc requires that we fall off the end of functions
 132         // that return values instead of using our own return
 133         // statements.
 134 }
 135
 136 // Must only be called from a single goroutine at a time.
 137 func signal_enable(s uint32) {
 138         int32 i;
 139
 140         if(!sig.inuse) {
 141                 // The first call to signal_enable is for us
 142                 // to use for initialization.  It does not pass
 143                 // signal information in m.
 144                 sig.inuse = true;       // enable reception of signals; cannot disable
 145                 runtime_noteclear(&sig);
 146                 return;
 147         }
 148
 149         if(~s == 0) {
 150                 // Special case: want everything.
 151                 for(i=0; (size_t)i<nelem(sig.wanted); i++)
 152                         sig.wanted[i] = ~(uint32)0;
 153                 runtime_sigenable(s);
 154                 return;
 155         }
 156
 157         if(s >= nelem(sig.wanted)*32)
 158                 return;
 159         sig.wanted[s/32] |= 1U<<(s&31);
 160         runtime_sigenable(s);
 161 }