--- a/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/ExecutionContext.java	Tue May 13 18:31:18 2014 -0700
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/ExecutionContext.java	Mon May 19 17:14:36 2014 -0700
@@ -27,31 +27,131 @@
 import java.util.*;
 
 import com.oracle.truffle.api.instrument.*;
+import com.oracle.truffle.api.instrument.impl.*;
 import com.oracle.truffle.api.source.*;
 
 /**
  * Access to information and basic services in the runtime context for a Truffle-implemented guest
  * language.
  * <p>
- * <strong>Disclaimer:</strong> this interface is under development and will change.
+ * <strong>Disclaimer:</strong> this class is under development and will change.
  */
-public interface ExecutionContext {
+public abstract class ExecutionContext {
+
+    private final ProbeManager probeManager = new ProbeManager();
+    private final SourceManager sourceManager = new SourceManager();
+    private final List<SourceListener> sourceListeners = new ArrayList<>();
+    private Visualizer visualizer = new DefaultVisualizer();
+
+    protected ExecutionContext() {
+    }
+
+    public void initialize() {
+        setSourceCallback(new SourceCallback() {
+
+            public void startLoading(Source source) {
+                for (SourceListener listener : sourceListeners) {
+                    listener.loadStarting(source);
+                }
+            }
+
+            public void endLoading(Source source) {
+                for (SourceListener listener : sourceListeners) {
+                    listener.loadEnding(source);
+                }
+            }
+        });
+    }
+
+    /**
+     * Gets access to source management services.
+     */
+    public final SourceManager getSourceManager() {
+        return sourceManager;
+    }
+
+    /**
+     * Registers a tool interested in being notified about the loading of {@link Source}s.
+     */
+    public final void addSourceListener(SourceListener listener) {
+        assert listener != null;
+        sourceListeners.add(listener);
+    }
+
+    /**
+     * Registers a tool interested in being notified about the insertion of a newly created
+     * {@link Probe} into a Truffle AST.
+     */
+    public final void addProbeListener(ProbeListener listener) {
+        probeManager.addProbeListener(listener);
+    }
+
+    /**
+     * Return the (possibly newly created) {@link Probe} uniquely associated with a particular
+     * source code location. A newly created probe carries no tags.
+     *
+     * @return a probe uniquely associated with an extent of guest language source code.
+     */
+    public final Probe getProbe(SourceSection sourceSection) {
+        return probeManager.getProbe(sourceSection);
+    }
+
+    /**
+     * Returns all existing probes with specific tag, or all probes if {@code tag = null}; empty
+     * collection if no probes found.
+     */
+    public final Collection<Probe> findProbesTaggedAs(PhylumTag tag) {
+        return probeManager.findProbesTaggedAs(tag);
+    }
+
+    /**
+     * Returns all existing probes with first character on a specified line; empty collection if no
+     * probes found.
+     */
+    public final Collection<Probe> findProbesByLine(SourceLineLocation lineLocation) {
+        return probeManager.findProbesByLine(lineLocation);
+    }
+
+    /**
+     * Sets a trap that will make a callback at any AST location where a existing probe holds a
+     * specified tag; only one trap may be set at a time.
+     *
+     * @throws IllegalStateException if a trap is already set
+     */
+    public final void setPhylumTrap(PhylumTrap trap) throws IllegalStateException {
+        // TODO (mlvdv) consider allowing multiple traps (without inhibiting Truffle inlining)
+        probeManager.setPhylumTrap(trap);
+    }
+
+    /**
+     * Clears a trap that will halt execution; only one trap may be set at a time.
+     *
+     * @throws IllegalStateException if no trap is set.
+     */
+    public final void clearPhylumTrap() {
+        probeManager.clearPhylumTrap();
+    }
+
+    /**
+     * Access to information visualization services for the specific language.
+     */
+    public final Visualizer getVisualizer() {
+        return visualizer;
+    }
+
+    /**
+     * Assign guest language-specific visualization support for tools. This must be assigned outside
+     * the implementation context to avoid build circularities.
+     */
+    public final void setVisualizer(Visualizer visualizer) {
+        this.visualizer = visualizer;
+    }
 
     /**
      * Gets the name of the language, possibly with version number. in short enough form that it
      * might be used for an interactive prompt.
      */
-    String getLanguageShortName();
-
-    /**
-     * Gets access to source management services.
-     */
-    SourceManager getSourceManager();
-
-    /**
-     * Registers a tool interested in being notified of events related to the loading of sources.
-     */
-    void addSourceListener(SourceListener listener);
+    public abstract String getLanguageShortName();
 
     /**
      * Add instrumentation to subsequently constructed Truffle ASTs for the guest language; every
@@ -60,51 +160,19 @@
      * @throws IllegalStateException if AST instrumentation not enabled
      * @throws IllegalArgumentException if prober not usable for the guest language implementation.
      */
-    void addNodeProber(ASTNodeProber nodeProber) throws IllegalStateException, IllegalArgumentException;
-
-    /**
-     * Registers a tool interested in being notified about the insertion of a newly created
-     * {@link Probe} into a Truffle AST.
-     */
-    void addProbeListener(ProbeListener listener);
-
-    /**
-     * Return the (possibly newly created) {@link Probe} uniquely associated with a particular
-     * source code location. A newly created probe carries no tags.
-     *
-     * @return a probe uniquely associated with an extent of guest language source code.
-     */
-    Probe getProbe(SourceSection sourceSection);
-
-    /**
-     * Returns all existing probes with specific tag, or all probes if {@code tag = null}; empty
-     * collection if no probes found.
-     */
-    Collection<Probe> findProbesTaggedAs(PhylumTag tag);
+    public abstract void addNodeProber(ASTNodeProber nodeProber) throws IllegalStateException, IllegalArgumentException;
 
     /**
-     * Returns all existing probes with first character on a specified line; empty collection if no
-     * probes found.
+     * Assigns a guest language-specific manager for using {@link ASTNodeProber}s added by tools to
+     * instrument ASTs with {@link Probe}s at specified nodes. This must be assigned outside the
+     * implementation context to avoid build circularities. It must also be set before any
+     * instrumentation probe implementations are assigned.
      */
-    Collection<Probe> findProbesByLine(SourceLineLocation lineLocation);
+    public abstract void setASTProber(ASTProber astProber);
 
     /**
-     * Sets a trap that will make a callback at any AST location where a existing probe holds a
-     * specified tag; only one trap may be set at a time.
-     *
-     * @throws IllegalStateException if a trap is already set
+     * Establishes source event reporting
      */
-    void setTrap(PhylumTrap trap) throws IllegalStateException;
+    protected abstract void setSourceCallback(SourceCallback sourceCallback);
 
-    /**
-     * Clears a trap that will halt execution; only one trap may be set at a time.
-     *
-     * @throws IllegalStateException if no trap is set.
-     */
-    void clearTrap() throws IllegalStateException;
-
-    /**
-     * Access to information visualization services for the specific language.
-     */
-    Visualizer getVisualizer();
 }