Replaces LongJump with LongJumpScope.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
===================================================================
--- runtime/vm/snapshot.cc	(revision 31413)
+++ runtime/vm/snapshot.cc	(working copy)
@@ -167,12 +167,10 @@
 
 
 RawObject* SnapshotReader::ReadObject() {
-  // Setup for long jump in case there is an exception while reading.
-  LongJump* base = isolate()->long_jump_base();
-  LongJump jump;
-  isolate()->set_long_jump_base(&jump);
   const Instance& null_object = Instance::Handle();
   *ErrorHandle() = UnhandledException::New(null_object, null_object);
+  // Setup for long jump in case there is an exception while reading.
+  LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     Object& obj = Object::Handle(ReadObjectImpl());
     for (intptr_t i = 0; i < backward_references_.length(); i++) {
@@ -181,13 +179,11 @@
         backward_references_[i]->set_state(kIsDeserialized);
       }
     }
-    isolate()->set_long_jump_base(base);
     return obj.raw();
   } else {
     // An error occurred while reading, return the error object.
     const Error& err = Error::Handle(isolate()->object_store()->sticky_error());
     isolate()->object_store()->clear_sticky_error();
-    isolate()->set_long_jump_base(base);
     return err.raw();
   }
 }
@@ -1082,9 +1078,7 @@
 
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
-  LongJump* base = isolate->long_jump_base();
-  LongJump jump;
-  isolate->set_long_jump_base(&jump);
+  LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     NoGCScope no_gc;
 
@@ -1101,10 +1095,7 @@
 
     FillHeader(kind());
     UnmarkAll();
-
-    isolate->set_long_jump_base(base);
   } else {
-    isolate->set_long_jump_base(base);
     ThrowException(exception_type(), exception_msg());
   }
 }
@@ -1475,9 +1466,7 @@
 
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
-  LongJump* base = isolate->long_jump_base();
-  LongJump jump;
-  isolate->set_long_jump_base(&jump);
+  LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Write out the library object.
     NoGCScope no_gc;
@@ -1485,9 +1474,7 @@
     WriteObject(lib.raw());
     FillHeader(kind());
     UnmarkAll();
-    isolate->set_long_jump_base(base);
   } else {
-    isolate->set_long_jump_base(base);
     ThrowException(exception_type(), exception_msg());
   }
 }
@@ -1512,16 +1499,12 @@
 
   // Setup for long jump in case there is an exception while writing
   // the message.
-  LongJump* base = isolate->long_jump_base();
-  LongJump jump;
-  isolate->set_long_jump_base(&jump);
+  LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
-    isolate->set_long_jump_base(base);
   } else {
-    isolate->set_long_jump_base(base);
     ThrowException(exception_type(), exception_msg());

[siva, 2014/01/03 21:18:35]

How does this work now for the ThrowException case,
The destructor for LongJumpScope will not run as it is not a
StackResource.

[zra, 2014/01/03 21:52:59]

I see two options:
1. Treat this as a special case and say something like:
{
  LongJumpScope jump;
  if (setjmp(*jump.Set()) == 0) {
    ...
    return;
  }
}
ThrowException();

Or

2. Split LongJumpScope into two classes: one that is a StackResource and only
maintains the long_jump_base, and one that is as before and only tracks the
other StackResources.

What sounds good?

[siva, 2014/01/04 00:04:22]

I prefer the first.

We can add an assertion in ThrowException to ensure that people
don't throw inside a current LongJumpScope.

On 2014/01/03 21:52:59, zra wrote:

   }
 }