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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
import org.mozilla.javascript.Context;
import org.mozilla.javascript.ContextFactory;
import org.mozilla.javascript.Script;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;
/** Example of controlling the JavaScript with multiple scopes and threads. */
public class DynamicScopes {
static boolean useDynamicScope;
static class MyFactory extends ContextFactory {
@Override
protected boolean hasFeature(Context cx, int featureIndex) {
if (featureIndex == Context.FEATURE_DYNAMIC_SCOPE) {
return useDynamicScope;
}
return super.hasFeature(cx, featureIndex);
}
}
static {
ContextFactory.initGlobal(new MyFactory());
}
/**
* Main entry point.
*
* <p>Set up the shared scope and then spawn new threads that execute relative to that shared
* scope. Try to run functions with and without dynamic scope to see the effect.
*
* <p>The expected output is
*
* <pre>
* sharedScope
* nested:sharedScope
* sharedScope
* nested:sharedScope
* sharedScope
* nested:sharedScope
* thread0
* nested:thread0
* thread1
* nested:thread1
* thread2
* nested:thread2
* </pre>
*
* The final three lines may be permuted in any order depending on thread scheduling.
*/
public static void main(String[] args) {
Context cx = Context.enter();
try {
// Precompile source only once
String source =
""
+ "var x = 'sharedScope';\n"
+ "function f() { return x; }\n"
// Dynamic scope works with nested function too
+ "function initClosure(prefix) {\n"
+ " return function test() { return prefix+x; }\n"
+ "}\n"
+ "var closure = initClosure('nested:');\n"
+ "";
Script script = cx.compileString(source, "sharedScript", 1, null);
useDynamicScope = false;
runScripts(cx, script);
useDynamicScope = true;
runScripts(cx, script);
} finally {
Context.exit();
}
}
static void runScripts(Context cx, Script script) {
// Initialize the standard objects (Object, Function, etc.)
// This must be done before scripts can be executed. The call
// returns a new scope that we will share.
ScriptableObject sharedScope = cx.initStandardObjects(null, true);
// Now we can execute the precompiled script against the scope
// to define x variable and f function in the shared scope.
script.exec(cx, sharedScope);
// Now we spawn some threads that execute a script that calls the
// function 'f'. The scope chain looks like this:
// <pre>
// ------------------ ------------------
// | per-thread scope | -prototype-> | shared scope |
// ------------------ ------------------
// ^
// |
// parentScope
// |
// ------------------
// | f's activation |
// ------------------
// </pre>
// Both the shared scope and the per-thread scope have variables 'x'
// defined in them. If 'f' is compiled with dynamic scope enabled,
// the 'x' from the per-thread scope will be used. Otherwise, the 'x'
// from the shared scope will be used. The 'x' defined in 'g' (which
// calls 'f') should not be seen by 'f'.
final int threadCount = 3;
Thread[] t = new Thread[threadCount];
for (int i = 0; i < threadCount; i++) {
String source2 =
""
+ "function g() { var x = 'local'; return f(); }\n"
+ "java.lang.System.out.println(g());\n"
+ "function g2() { var x = 'local'; return closure(); }\n"
+ "java.lang.System.out.println(g2());\n"
+ "";
t[i] = new Thread(new PerThread(sharedScope, source2, "thread" + i));
}
for (int i = 0; i < threadCount; i++) t[i].start();
// Don't return in this thread until all the spawned threads have
// completed.
for (int i = 0; i < threadCount; i++) {
try {
t[i].join();
} catch (InterruptedException e) {
}
}
}
static class PerThread implements Runnable {
PerThread(Scriptable sharedScope, String source, String x) {
this.sharedScope = sharedScope;
this.source = source;
this.x = x;
}
@Override
public void run() {
// We need a new Context for this thread.
Context cx = Context.enter();
try {
// We can share the scope.
Scriptable threadScope = cx.newObject(sharedScope);
threadScope.setPrototype(sharedScope);
// We want "threadScope" to be a new top-level
// scope, so set its parent scope to null. This
// means that any variables created by assignments
// will be properties of "threadScope".
threadScope.setParentScope(null);
// Create a JavaScript property of the thread scope named
// 'x' and save a value for it.
threadScope.put("x", threadScope, x);
cx.evaluateString(threadScope, source, "threadScript", 1, null);
} finally {
Context.exit();
}
}
private Scriptable sharedScope;
private String source;
private String x;
}
}
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