Fix background compilation: allocate stubs at safepoint

runtime/vm/stub_code.cc

Index: runtime/vm/stub_code.cc
diff --git a/runtime/vm/stub_code.cc b/runtime/vm/stub_code.cc
index d06b125ee61bef3d586c12ac25bea40a0c138edf..14cd572f52fc275d60e4013a37dfaf68c1679bde 100644
--- a/runtime/vm/stub_code.cc
+++ b/runtime/vm/stub_code.cc
@@ -7,6 +7,7 @@
 #include "platform/assert.h"
 #include "platform/globals.h"
 #include "vm/assembler.h"
+#include "vm/compiler.h"  // SafepointOperationScope.

[siva, 2016/02/17 21:07:49]

#include "vm/safepoint.h"

(SafepointOperationScope is defined here).

[srdjan, 2016/02/17 21:15:14]

Done.

 #include "vm/disassembler.h"
 #include "vm/flags.h"
 #include "vm/object_store.h"
@@ -120,9 +121,33 @@ RawCode* StubCode::GetAllocationStubForClass(const Class& cls) {
     Assembler assembler;
     const char* name = cls.ToCString();
     StubCode::GenerateAllocationStubForClass(&assembler, cls);
-    stub ^= Code::FinalizeCode(name, &assembler, false /* optimized */);
-    stub.set_owner(cls);
-    cls.set_allocation_stub(stub);
+
+    if (thread->IsMutatorThread()) {
+      stub ^= Code::FinalizeCode(name, &assembler, false /* optimized */);
+      stub.set_owner(cls);
+      cls.set_allocation_stub(stub);
+    } else {
+      // This part of compilation must be at a safepoint.

[siva, 2016/02/17 21:07:49]

This part of stub code generation must be at a safepoint.

[srdjan, 2016/02/17 21:15:15]

Done.

+      // Stop mutator thread before creating the instruction object and
+      // installing code.
+      // Mutator thread may not run code while we are creating the
+      // instruction object, since the creation of instruction object
+      // changes code page access permissions (makes them temporary not
+      // executable).
+      {
+        SafepointOperationScope safepoint_scope(thread);
+        // Do not Garbage collect during this stage and instead allow the
+        // heap to grow.
+        NoHeapGrowthControlScope no_growth_control;
+        stub ^= Code::FinalizeCode(name, &assembler, false /* optimized */);
+        stub.set_owner(cls);
+        cls.set_allocation_stub(stub);
+      }
+      Isolate* isolate = thread->isolate();
+      if (isolate->heap()->NeedsGarbageCollection()) {
+        isolate->heap()->CollectAllGarbage();
+      }
+    }

[siva, 2016/02/17 21:07:49]

I am wondering if it makes sense to move this to Code::FinalizeCode instead of
repeating it twice here and in the compiler.

[srdjan, 2016/02/17 21:15:15]

The situations are not exactly identical. Leaving it as it is.

     if (FLAG_support_disassembler && FLAG_disassemble_stubs) {
       LogBlock lb;
       THR_Print("Code for allocation stub '%s': {\n", name);