context.java

這是一個javascript 的 interpreter是了解 web browser的好材料

     * ContextFactory instance.
     * @deprecated use {@link ContextFactory#enter()} or 
     * {@link ContextFactory#call(ContextAction)} instead as this method relies
     * on usage of a static singleton "global" ContextFactory.
     * @return a Context associated with the current thread
     * @see #getCurrentContext()
     * @see #exit()
     * @see #call(ContextAction)
     */
    public static Context enter()
    {
        return enter(null);
    }

    /**
     * Get a Context associated with the current thread, using
     * the given Context if need be.
     * <p>
     * The same as <code>enter()</code> except that <code>cx</code>
     * is associated with the current thread and returned if
     * the current thread has no associated context and <code>cx</code>
     * is not associated with any other thread.
     * @param cx a Context to associate with the thread if possible
     * @return a Context associated with the current thread
     * @deprecated use {@link ContextFactory#enterContext(Context)} instead as 
     * this method relies on usage of a static singleton "global" ContextFactory.
     * @see ContextFactory#enterContext(Context)
     * @see ContextFactory#call(ContextAction)
     */
    public static Context enter(Context cx)
    {
        return enter(cx, ContextFactory.getGlobal());
    }
    
    static final Context enter(Context cx, ContextFactory factory)
    {
        Object helper = VMBridge.instance.getThreadContextHelper();
        Context old = VMBridge.instance.getContext(helper);
        if (old != null) {
            cx = old;
        } else {
            if (cx == null) {
                cx = factory.makeContext();
                if (cx.enterCount != 0) {
                    throw new IllegalStateException("factory.makeContext() returned Context instance already associated with some thread");
                }
                factory.onContextCreated(cx);
                if (factory.isSealed() && !cx.isSealed()) {
                    cx.seal(null);
                }
            } else {
                if (cx.enterCount != 0) {
                    throw new IllegalStateException("can not use Context instance already associated with some thread");
                }
            }
            VMBridge.instance.setContext(helper, cx);
        }
        ++cx.enterCount;
        return cx;
     }

    /**
     * Exit a block of code requiring a Context.
     *
     * Calling <code>exit()</code> will remove the association between
     * the current thread and a Context if the prior call to
     * {@link ContextFactory#enterContext()} on this thread newly associated a 
     * Context with this thread. Once the current thread no longer has an 
     * associated Context, it cannot be used to execute JavaScript until it is 
     * again associated with a Context.
     * @see ContextFactory#enterContext()
     */
    public static void exit()
    {
        Object helper = VMBridge.instance.getThreadContextHelper();
        Context cx = VMBridge.instance.getContext(helper);
        if (cx == null) {
            throw new IllegalStateException(
                "Calling Context.exit without previous Context.enter");
        }
        if (cx.enterCount < 1) Kit.codeBug();
        if (--cx.enterCount == 0) {
            VMBridge.instance.setContext(helper, null);
            cx.factory.onContextReleased(cx);
        }
    }
    
    /**
     * Call {@link ContextAction#run(Context cx)}
     * using the Context instance associated with the current thread.
     * If no Context is associated with the thread, then
     * <tt>ContextFactory.getGlobal().makeContext()</tt> will be called to
     * construct new Context instance. The instance will be temporary
     * associated with the thread during call to
     * {@link ContextAction#run(Context)}.
     * @deprecated use {@link ContextFactory#call(ContextAction)} instead as 
     * this method relies on usage of a static singleton "global" 
     * ContextFactory.
     * @return The result of {@link ContextAction#run(Context)}.
     */
    public static Object call(ContextAction action)
    {
        return call(ContextFactory.getGlobal(), action);
    }

    /**
     * Call {@link
     * Callable#call(Context cx, Scriptable scope, Scriptable thisObj,
     *               Object[] args)}
     * using the Context instance associated with the current thread.
     * If no Context is associated with the thread, then
     * {@link ContextFactory#makeContext()} will be called to construct
     * new Context instance. The instance will be temporary associated
     * with the thread during call to {@link ContextAction#run(Context)}.
     * <p>
     * It is allowed but not advisable to use null for <tt>factory</tt> 
     * argument in which case the global static singleton ContextFactory 
     * instance will be used to create new context instances.
     * @see ContextFactory#call(ContextAction)
     */
    public static Object call(ContextFactory factory, final Callable callable,
                              final Scriptable scope, final Scriptable thisObj,
                              final Object[] args)
    {
        if(factory == null) {
            factory = ContextFactory.getGlobal();
        }
        return call(factory, new ContextAction() {
            public Object run(Context cx) {
                return callable.call(cx, scope, thisObj, args);
            }
        });
    }
    
    /**
     * The method implements {@links ContextFactory#call(ContextAction)} logic.
     */
    static Object call(ContextFactory factory, ContextAction action) {
        Context cx = enter(null, factory);
        try {
            return action.run(cx);
        }
        finally {
            exit();
        }
    }

    /**
     * @deprecated
     * @see ContextFactory#addListener(ContextFactory.Listener)
     * @see ContextFactory#getGlobal()
     */
    public static void addContextListener(ContextListener listener)
    {
        // Special workaround for the debugger
        String DBG = "org.mozilla.javascript.tools.debugger.Main";
        if (DBG.equals(listener.getClass().getName())) {
            Class cl = listener.getClass();
            Class factoryClass = Kit.classOrNull(
                "org.mozilla.javascript.ContextFactory");
            Class[] sig = { factoryClass };
            Object[] args = { ContextFactory.getGlobal() };
            try {
                Method m = cl.getMethod("attachTo", sig);
                m.invoke(listener, args);
            } catch (Exception ex) {
                RuntimeException rex = new RuntimeException();
                Kit.initCause(rex, ex);
                throw rex;
            }
            return;
        }

        ContextFactory.getGlobal().addListener(listener);
    }

    /**
     * @deprecated
     * @see ContextFactory#removeListener(ContextFactory.Listener)
     * @see ContextFactory#getGlobal()
     */
    public static void removeContextListener(ContextListener listener)
    {
        ContextFactory.getGlobal().addListener(listener);
    }

    /**
     * Return {@link ContextFactory} instance used to create this Context.
     */
    public final ContextFactory getFactory()
    {
        return factory;
    }

    /**
     * Checks if this is a sealed Context. A sealed Context instance does not
     * allow to modify any of its properties and will throw an exception
     * on any such attempt.
     * @see #seal(Object sealKey)
     */
    public final boolean isSealed()
    {
        return sealed;
    }

    /**
     * Seal this Context object so any attempt to modify any of its properties
     * including calling {@link #enter()} and {@link #exit()} methods will
     * throw an exception.
     * <p>
     * If <tt>sealKey</tt> is not null, calling
     * {@link #unseal(Object sealKey)} with the same key unseals
     * the object. If <tt>sealKey</tt> is null, unsealing is no longer possible.
     *
     * @see #isSealed()
     * @see #unseal(Object)
     */
    public final void seal(Object sealKey)
    {
        if (sealed) onSealedMutation();
        sealed = true;
        this.sealKey = sealKey;
    }

    /**
     * Unseal previously sealed Context object.
     * The <tt>sealKey</tt> argument should not be null and should match
     * <tt>sealKey</tt> suplied with the last call to
     * {@link #seal(Object)} or an exception will be thrown.
     *
     * @see #isSealed()
     * @see #seal(Object sealKey)
     */
    public final void unseal(Object sealKey)
    {
        if (sealKey == null) throw new IllegalArgumentException();
        if (this.sealKey != sealKey) throw new IllegalArgumentException();
        if (!sealed) throw new IllegalStateException();
        sealed = false;
        this.sealKey = null;
    }

    static void onSealedMutation()
    {
        throw new IllegalStateException();
    }

    /**
     * Get the current language version.
     * <p>
     * The language version number affects JavaScript semantics as detailed
     * in the overview documentation.
     *
     * @return an integer that is one of VERSION_1_0, VERSION_1_1, etc.
     */
    public final int getLanguageVersion()
    {
       return version;
    }

    /**
     * Set the language version.
     *
     * <p>
     * Setting the language version will affect functions and scripts compiled
     * subsequently. See the overview documentation for version-specific
     * behavior.
     *
     * @param version the version as specified by VERSION_1_0, VERSION_1_1, etc.
     */
    public void setLanguageVersion(int version)
    {
        if (sealed) onSealedMutation();
        checkLanguageVersion(version);
        Object listeners = propertyListeners;
        if (listeners != null && version != this.version) {
            firePropertyChangeImpl(listeners, languageVersionProperty,
                               new Integer(this.version),
                               new Integer(version));
        }
        this.version = version;
    }

    public static boolean isValidLanguageVersion(int version)
    {
        switch (version) {
            case VERSION_DEFAULT:
            case VERSION_1_0:
            case VERSION_1_1:
            case VERSION_1_2:
            case VERSION_1_3:
            case VERSION_1_4:
            case VERSION_1_5:
            case VERSION_1_6:
            case VERSION_1_7:
                return true;
        }
        return false;
    }

    public static void checkLanguageVersion(int version)
    {
        if (isValidLanguageVersion(version)) {
            return;
        }
        throw new IllegalArgumentException("Bad language version: "+version);
    }

    /**
     * Get the implementation version.
     *
     * <p>
     * The implementation version is of the form
     * <pre>
     *    "<i>name langVer</i> <code>release</code> <i>relNum date</i>"
     * </pre>
     * where <i>name</i> is the name of the product, <i>langVer</i> is
     * the language version, <i>relNum</i> is the release number, and
     * <i>date</i> is the release date for that specific
     * release in the form "yyyy mm dd".
     *
     * @return a string that encodes the product, language version, release
     *         number, and date.
     */
    public final String getImplementationVersion()
    {
        // XXX Probably it would be better to embed this directly into source
        // with special build preprocessing but that would require some ant
        // tweaking and then replacing token in resource files was simpler
        if (implementationVersion == null) {
            implementationVersion
                = ScriptRuntime.getMessage0("implementation.version");
        }
        return implementationVersion;
    }

    /**
     * Get the current error reporter.
     *
     * @see org.mozilla.javascript.ErrorReporter
     */
    public final ErrorReporter getErrorReporter()
    {
        if (errorReporter == null) {
            return DefaultErrorReporter.instance;
        }
        return errorReporter;
    }

    /**
     * Change the current error reporter.
     *
     * @return the previous error reporter
     * @see org.mozilla.javascript.ErrorReporter
     */
    public final ErrorReporter setErrorReporter(ErrorReporter reporter)
    {
        if (sealed) onSealedMutation();