Safepoint interface and unit tests.

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
diff --git a/runtime/vm/code_generator.cc b/runtime/vm/code_generator.cc
index dd977b239684252db484eb32a0e25e3a92e5da2d..cdb7d40b12a7d7293f592f08849137f1b331ea95 100644
--- a/runtime/vm/code_generator.cc
+++ b/runtime/vm/code_generator.cc
@@ -23,6 +23,7 @@
 #include "vm/runtime_entry.h"
 #include "vm/stack_frame.h"
 #include "vm/symbols.h"
+#include "vm/thread_registry.h"
 #include "vm/verifier.h"
 
 namespace dart {
@@ -1299,6 +1300,10 @@ DEFINE_RUNTIME_ENTRY(StackOverflow, 0) {
   }
 
   uword interrupt_bits = isolate->GetAndClearInterrupts();
+  if ((interrupt_bits & Isolate::kSafepointInterrrupt) != 0) {
+    isolate->thread_registry()->CheckSafepoint();

[Ivan Posva, 2015/07/31 20:28:09]

Regardless of the interrupt reason we should check for pending safepoint
rendezvous. Before throwing stack overflow exceptions and other code which can
consume an arbitrary time.

[koda, 2015/07/31 22:40:44]

Done by creating single VM interrupt for all these kinds of checks. The new
version also avoids scheduling redundant GC when the store buffer is no longer
overflowed after the CheckSafepoint.

+    // TODO(koda): Merge safepoint + store buffer into simply "GC interrupt"?
+  }
   if ((interrupt_bits & Isolate::kStoreBufferInterrupt) != 0) {
     if (FLAG_verbose_gc) {
       OS::PrintErr("Scavenge scheduled by store buffer overflow.\n");