- Implement Isolate.pause and Isolate.resume.

runtime/vm/message_handler.h

Index: runtime/vm/message_handler.h
===================================================================
--- runtime/vm/message_handler.h	(revision 37860)
+++ runtime/vm/message_handler.h	(working copy)
@@ -71,6 +71,11 @@
     return control_ports_;
   }
 
+  bool paused() const { return paused_ > 0; }
+
+  void increment_paused() { paused_++; }

[siva, 2014/07/01 21:42:56]

How do we ensure paused does not overflow?

[Lasse Reichstein Nielsen, 2014/07/02 08:11:55]

If paused_ is an intptr_t, and we store one resumeCapability per pause, we will
definitely run out of memory before it overflows.

[siva, 2014/07/02 14:52:10]

True but instead of relying on that one needs to set a max possible value for
this and check against that max like we do in all other similar scenarios in the
VM. That is the recommended guideline from the security folks.

[Ivan Posva, 2014/07/03 12:51:17]

Isolate::AddResumeCapability now prevents overflows of this counter by
calculating a maximum allowable number of capabilities recorded and not growing
once that number is reached.

+  void decrement_paused() { paused_--; }

[siva, 2014/07/01 21:42:56]

ASSERT(paused_ > 0);

[Ivan Posva, 2014/07/03 12:51:17]

Done.

+
   bool pause_on_start() const {
     return pause_on_start_;
   }
@@ -164,6 +169,7 @@
   MessageQueue* oob_queue_;
   intptr_t control_ports_;  // The number of open control ports usually 0 or 1.
   intptr_t live_ports_;  // The number of open ports, including control ports.
+  intptr_t paused_;  // The number of pause messages received.
   bool pause_on_start_;
   bool pause_on_exit_;
   bool paused_on_exit_;