Re: [rvm-research] Writing information into Object Header's Misc field when object created

Rifat Shahriyar <[email protected]>
Newsgroups gmane.comp.java.jikes.rvm.devel
Message-ID <[email protected]> 
Hi,
The attached patch (can be applied on the current tip) demonstrate how 
to read/write misc header when an object is created. It may help you.

Regards
-
Rifat
Australian National University


On 27/06/2014 1:30 am, Matthew Ma wrote:
> Hi,
> I want to write information into Object Header's Misc field when an 
> object is created: modify where RVM create new object (and its hearde)
>
> eg. From the user annotated program, I want to write group information 
> into the object header (ast and bst all refers to Tree object but each 
> would have different Group number written into the object header)
>
> 1 @create("Group1") //GroupInformation
> 2 public void foo(){
> 3ast = new Tree();
> 4 }
>
> 5 @create("Group2") ////GroupInformation
> 6 public void foo(){
> 7bst = new Tree();
> 8 }
>
> I looked into the option of changing the RVM to handle this mechanism 
> when object created, but from RVMClass, I could't find direct 
> connection to how to access MiscHeader class.
> In ObjectModel.java, I saw MiscHeader is invoked with 
> initializeHeader(..) at allocateScalar. is it where I can write 
> GroupInformation into the misc header field (by using RVMClass to get 
> current running RVMMethod, and use getAnnotation() to obtain the 
> annotated Group Information)?
>
> Thanks,
>
> Matthew
>
>
>
>
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Turn processes into business applications with Bonita BPM Community Edition
Quickly connect people, data, and systems into organized workflows
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http://p.sf.net/sfu/Bonitasoft

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mischeader.patch (text/plain, 4.8 KB) 
diff -r 25e90303047f rvm/src/org/jikesrvm/mm/mminterface/MemoryManager.java
--- a/rvm/src/org/jikesrvm/mm/mminterface/MemoryManager.java	Wed Jun 18 20:05:08 2014 +0200
+++ b/rvm/src/org/jikesrvm/mm/mminterface/MemoryManager.java	Fri Jun 27 17:39:15 2014 +1000
@@ -487,6 +487,8 @@
     Address region = allocateSpace(mutator, size, align, offset, allocator, site);
     Object result = ObjectModel.initializeScalar(region, tib, size);
     mutator.postAlloc(ObjectReference.fromObject(result), ObjectReference.fromObject(tib), size, allocator);
+    ObjectModel.writeMisc(ObjectReference.fromObject(result), Word.one());
+    if (VM.VerifyAssertions) VM._assert(ObjectModel.readMisc(ObjectReference.fromObject(result)).EQ(Word.one()));
     return result;
   }
 
@@ -553,6 +555,8 @@
     Address region = allocateSpace(mutator, size, align, offset, allocator, site);
     Object result = ObjectModel.initializeArray(region, tib, numElements, size);
     mutator.postAlloc(ObjectReference.fromObject(result), ObjectReference.fromObject(tib), size, allocator);
+    ObjectModel.writeMisc(ObjectReference.fromObject(result), Word.one());
+    if (VM.VerifyAssertions) VM._assert(ObjectModel.readMisc(ObjectReference.fromObject(result)).EQ(Word.one()));
     return result;
   }
 
@@ -842,7 +846,9 @@
 
     Object result = ObjectModel.initializeArray(region, fakeTib, elements, size);
     mutator.postAlloc(ObjectReference.fromObject(result), ObjectReference.fromObject(fakeTib), size, type.getMMAllocator());
-
+    ObjectModel.writeMisc(ObjectReference.fromObject(result), Word.one());
+    if (VM.VerifyAssertions) VM._assert(ObjectModel.readMisc(ObjectReference.fromObject(result)).EQ(Word.one()));
+    
     /* Now we replace the TIB */
     ObjectModel.setTIB(result, realTib);
 
diff -r 25e90303047f rvm/src/org/jikesrvm/objectmodel/JavaHeaderConstants.java
--- a/rvm/src/org/jikesrvm/objectmodel/JavaHeaderConstants.java	Wed Jun 18 20:05:08 2014 +0200
+++ b/rvm/src/org/jikesrvm/objectmodel/JavaHeaderConstants.java	Fri Jun 27 17:39:15 2014 +1000
@@ -44,7 +44,7 @@
   /** Number of bytes used by the Java Header */
   int JAVA_HEADER_BYTES = TIB_BYTES + STATUS_BYTES;
   /** Number of bytes used by the GC Header */
-  int GC_HEADER_BYTES = MemoryManagerConstants.GC_HEADER_BYTES;
+  int GC_HEADER_BYTES = MemoryManagerConstants.GC_HEADER_BYTES + BYTES_IN_ADDRESS;
   /** Number of bytes used by the miscellaneous header */
   int MISC_HEADER_BYTES = MiscHeaderConstants.NUM_BYTES_HEADER;
   /** Size of GC and miscellaneous headers */
diff -r 25e90303047f rvm/src/org/jikesrvm/objectmodel/MiscHeader.java
--- a/rvm/src/org/jikesrvm/objectmodel/MiscHeader.java	Wed Jun 18 20:05:08 2014 +0200
+++ b/rvm/src/org/jikesrvm/objectmodel/MiscHeader.java	Fri Jun 27 17:39:15 2014 +1000
@@ -37,8 +37,9 @@
 
   private static final Offset MISC_HEADER_START = JavaHeaderConstants.MISC_HEADER_OFFSET;
 
+  static final Offset MY_MISC_OFFSET = MISC_HEADER_START;
   /* offset from object ref to .oid field, in bytes */
-  static final Offset OBJECT_OID_OFFSET = MISC_HEADER_START;
+  static final Offset OBJECT_OID_OFFSET = MY_MISC_OFFSET.plus(BYTES_IN_ADDRESS);
   /* offset from object ref to OBJECT_DEATH field, in bytes */
   static final Offset OBJECT_DEATH_OFFSET = OBJECT_OID_OFFSET.plus(BYTES_IN_ADDRESS);
   /* offset from object ref to .link field, in bytes */
@@ -212,4 +213,12 @@
       VM.sysWrite(" DEATH=", getDeathTime(ref));
     }
   }
+  
+  public static void writeMisc(ObjectReference object, Word value) {
+    Magic.setWordAtOffset(object, MY_MISC_OFFSET, value);
+  }
+  
+  public static Word readMisc(ObjectReference object) {
+    return Magic.getWordAtOffset(object, MY_MISC_OFFSET);
+  }
 }
diff -r 25e90303047f rvm/src/org/jikesrvm/objectmodel/MiscHeaderConstants.java
--- a/rvm/src/org/jikesrvm/objectmodel/MiscHeaderConstants.java	Wed Jun 18 20:05:08 2014 +0200
+++ b/rvm/src/org/jikesrvm/objectmodel/MiscHeaderConstants.java	Fri Jun 27 17:39:15 2014 +1000
@@ -36,5 +36,5 @@
   /**
    * How many bytes are used by all misc header fields?
    */
-  int NUM_BYTES_HEADER = GC_TRACING_HEADER_BYTES; // + YYY_HEADER_BYTES;
+  int NUM_BYTES_HEADER = GC_TRACING_HEADER_BYTES + BYTES_IN_ADDRESS; // + YYY_HEADER_BYTES;
 }
diff -r 25e90303047f rvm/src/org/jikesrvm/objectmodel/ObjectModel.java
--- a/rvm/src/org/jikesrvm/objectmodel/ObjectModel.java	Wed Jun 18 20:05:08 2014 +0200
+++ b/rvm/src/org/jikesrvm/objectmodel/ObjectModel.java	Fri Jun 27 17:39:15 2014 +1000
@@ -920,6 +920,14 @@
   public static void baselineEmitLoadTIB(Assembler asm, int dest, int object) {
     JavaHeader.baselineEmitLoadTIB(asm, dest, object);
   }
+  
+  public static void writeMisc(ObjectReference object, Word value) {
+    MiscHeader.writeMisc(object, value);
+  }
+  
+  public static Word readMisc(ObjectReference object) {
+    return MiscHeader.readMisc(object);
+  }
 }
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