SI-8362: Support for Future without sun.misc.Unsafe.

mchv · mchv · commit 30a6b6942b31 · 2015-02-17T12:26:38.000Z
Instead of using AtomicReferenceFieldUpdater extends directly AtomicReference as AtomicReferenceFieldUpdater.compareAndSet() isn't necessarily even inlined by Hotspot, while AtomicReference.compareAndSet() should be compiled down to the machine's CAS instruction.
The implementation is similar to the 2.12.x branch’s one.

Add an exclusion rule for mima to not check backward and forward compatibility as the class is package protected and in an imp package.
diff --git a/bincompat-backward.whitelist.conf b/bincompat-backward.whitelist.conf
@@ -208,6 +208,11 @@ filter {
     {
         matchName="scala.reflect.io.ZipArchive.scala$reflect$io$ZipArchive$$walkIterator"
         problemName=MissingMethodProblem
-    }
+    },
+    // SI-8362 - package-protected class in an impl package
+    {
+        matchName="scala.concurrent.impl.Promise$DefaultPromise"
+        problemName=MissingTypesProblem
+    } 
   ]
 }
diff --git a/bincompat-forward.whitelist.conf b/bincompat-forward.whitelist.conf
@@ -314,6 +314,11 @@ filter {
     {
         matchName="scala.reflect.runtime.Settings#IntSetting.valueSetByUser"
         problemName=MissingMethodProblem
-    }
+    },
+    // see SI-8362 - package-protected class in an impl package
+    {
+        matchName="scala.concurrent.impl.Promise$DefaultPromise"
+        problemName=MissingTypesProblem
+    } 
   ]
 }
diff --git a/src/library/scala/concurrent/impl/AbstractPromise.java b/src/library/scala/concurrent/impl/AbstractPromise.java
@@ -9,51 +9,17 @@
 package scala.concurrent.impl;
 
 
-import scala.concurrent.util.Unsafe;
-import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+import java.util.concurrent.atomic.AtomicReference;
 
 
 
-abstract class AbstractPromise {
-    private volatile Object _ref;
-
-    final static long _refoffset;
-    /*
-     * In a runtime with a security manager installed, or a non-Oracle runtime,
-     * the Unsafe class may be unavailable. In this case, _refoffset will be
-     * set to -1.
-     *
-     * We assume that a valid field offset will be non-negative, and likely a
-     * multiple of 4.
-     */
-    static {
-    	long refoffset = -1;
-	try {
-	    refoffset = Unsafe.instance.objectFieldOffset(AbstractPromise.class.getDeclaredField("_ref"));
-	} catch (Throwable t) {
-	    /* Unsafe object instance access failed */
-	}
-	_refoffset = refoffset;
-    }
+abstract class AbstractPromise extends AtomicReference<Object> {
     
-    /*
-     * The Hotspot compiler can identify that the value of _refoffset never
-     * changes, and compile only the branch below that is used. When the Unsafe
-     * object is available, the compare-and-swap operation will be inlined
-     * directly into *this* method's caller.
-     */
     protected final boolean updateState(Object oldState, Object newState) {
-    	if (_refoffset == -1) {
-	    return updater.compareAndSet(this, oldState, newState);
-	} else {
-	    return Unsafe.instance.compareAndSwapObject(this, _refoffset, oldState, newState);
-	}
+        return compareAndSet(oldState, newState);
     }
 
     protected final Object getState() {
-	return _ref;
+        return get();
     }
-
-    protected final static AtomicReferenceFieldUpdater<AbstractPromise, Object> updater =
-	AtomicReferenceFieldUpdater.newUpdater(AbstractPromise.class, Object.class, "_ref");
 }

Original file line number	Diff line number	Diff line change
`@@ -208,6 +208,11 @@ filter {`
`208`	`208`	`{`
`209`	`209`	`matchName="scala.reflect.io.ZipArchive.scala$reflect$io$ZipArchive$$walkIterator"`
`210`	`210`	`problemName=MissingMethodProblem`
`211`		`- }`
	`211`	`+ },`
	`212`	`+ // SI-8362 - package-protected class in an impl package`
	`213`	`+ {`
	`214`	`+ matchName="scala.concurrent.impl.Promise$DefaultPromise"`
	`215`	`+ problemName=MissingTypesProblem`
	`216`	`+ }`
`212`	`217`	`]`
`213`	`218`	`}`
Original file line number	Diff line number	Diff line change
`@@ -314,6 +314,11 @@ filter {`
`314`	`314`	`{`
`315`	`315`	`matchName="scala.reflect.runtime.Settings#IntSetting.valueSetByUser"`
`316`	`316`	`problemName=MissingMethodProblem`
`317`		`- }`
	`317`	`+ },`
	`318`	`+ // see SI-8362 - package-protected class in an impl package`
	`319`	`+ {`
	`320`	`+ matchName="scala.concurrent.impl.Promise$DefaultPromise"`
	`321`	`+ problemName=MissingTypesProblem`
	`322`	`+ }`
`318`	`323`	`]`
`319`	`324`	`}`