code review 131580043: runtime: Start and stop individual goroutines at gc saf...

src/pkg/runtime/stack.c

 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 #include "runtime.h"
 #include "arch_GOARCH.h"
 #include "malloc.h"
 #include "stack.h"
 #include "funcdata.h"
 #include "typekind.h"
@@ skipping 909 matching lines @@
                 runtime·throw("runtime: stack growth argsize");
         }
 
         if(gp->stackguard0 == (uintptr)StackPreempt) {
                 if(gp == g->m->g0)
                         runtime·throw("runtime: preempt g0");
                 if(oldstatus == Grunning && g->m->p == nil && g->m->locks == 0)
                         runtime·throw("runtime: g is running but p is not");
                 if(oldstatus == Gsyscall && g->m->locks == 0)
                         runtime·throw("runtime: stack growth during syscall");
+                if(oldstatus == Grunning && gp->preemptscan) {
+                        runtime·gcphasework(gp);
+                        runtime·casgstatus(gp, Gwaiting, Grunning);
+                        gp->stackguard0 = gp->stackguard;
+                        gp->preempt = false;·
+                        gp->preemptscan = false;        // Tells the GC premption was successful.
+                        runtime·gogo(&gp->sched);       // never return·
+                }
 
                 // Be conservative about where we preempt.
                 // We are interested in preempting user Go code, not runtime code.
                 if(oldstatus != Grunning || g->m->locks || g->m->mallocing || g->m->gcing || g->m->p->status != Prunning) {
                         // Let the goroutine keep running for now.
                         // gp->preempt is set, so it will be preempted next time.
                         gp->stackguard0 = gp->stackguard;
                         runtime·casgstatus(gp, Gwaiting, oldstatus); // oldstatus is Gsyscall or Grunning
                         runtime·gogo(&gp->sched);       // never return
                 }
@@ skipping 158 matching lines @@
         if(gp->m != nil && gp->m->libcallsp != 0)
                 return;
 #endif
         if(StackDebug > 0)
                 runtime·printf("shrinking stack %D->%D\n", (uint64)oldsize, (uint64)newsize);
         nframes = copyabletopsegment(gp);
         if(nframes == -1)
                 return;
         copystack(gp, nframes, newsize);
 }