Add support for interrupting an isolate in the vm. Interrupts are

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
===================================================================
--- runtime/vm/isolate.cc	(revision 2291)
+++ runtime/vm/isolate.cc	(working copy)
@@ -61,7 +61,9 @@
       debugger_(NULL),
       long_jump_base_(NULL),
       timer_list_(),
+      mutex_(new Mutex()),
       stack_limit_(0),
+      saved_stack_limit_(0),
       ast_node_id_(AstNode::kNoId) {
 }
 
@@ -75,6 +77,8 @@
   delete api_state_;
   delete stub_code_;
   delete code_index_table_;
+  delete mutex_;
+  mutex_ = NULL;  // Fail fast if interrupts are scheduled on a dead isolate.
 }
 
 
@@ -151,10 +155,37 @@
 
 
 void Isolate::SetStackLimit(uword limit) {
+  MutexLocker ml(mutex_);
   stack_limit_ = limit;
+  saved_stack_limit_ = limit;
 }
 
 
+void Isolate::ScheduleInterrupts(uword interrupt_bits) {
+  // TODO(turnidge): Can't use MutexLocker here because MutexLocker is
+  // a StackResource, which requires a current isolate.  Should
+  // MutexLocker really be a StackResource?
+  mutex_->Lock();
+  ASSERT((interrupt_bits & ~kInterruptsMask) == 0);  // Must fit in mask.
+  if (stack_limit_ == saved_stack_limit_) {
+    stack_limit_ = ((uword) -1) & ~kInterruptsMask;
+  }
+  stack_limit_ |= interrupt_bits;
+  mutex_->Unlock();
+}
+
+
+uword Isolate::GetAndClearInterrupts() {
+  MutexLocker ml(mutex_);
+  if (stack_limit_ == saved_stack_limit_) {
+    return 0;  // No interrupt was requested.
+  }
+  uword interrupt_bits = stack_limit_ & kInterruptsMask;
+  stack_limit_ = saved_stack_limit_;
+  return interrupt_bits;
+}
+
+
 static int MostCalledFunctionFirst(const Function* const* a,
                                    const Function* const* b) {
   if ((*a)->invocation_counter() > (*b)->invocation_counter()) {
@@ -230,6 +261,7 @@
 
 
 Dart_IsolateCreateCallback Isolate::create_callback_ = NULL;
+Dart_IsolateInterruptCallback Isolate::interrupt_callback_ = NULL;
 
 
 void Isolate::SetCreateCallback(Dart_IsolateCreateCallback cb) {
@@ -242,6 +274,16 @@
 }
 
 
+void Isolate::SetInterruptCallback(Dart_IsolateInterruptCallback cb) {
+  interrupt_callback_ = cb;
+}
+
+
+Dart_IsolateInterruptCallback Isolate::InterruptCallback() {
+  return interrupt_callback_;
+}
+
+
 void Isolate::StandardRunLoop() {
   ASSERT(long_jump_base() != NULL);
   ASSERT(post_message_callback() == &StandardPostMessageCallback);