runtime.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 496 行 · 第 1/2 页

     */
    public native long totalMemory();

    /**
     * Runs the garbage collector.
     * Calling this method suggests that the Java Virtual Machine expend 
     * effort toward recycling unused objects in order to make the memory 
     * they currently occupy available for quick reuse. When control 
     * returns from the method call, the Java Virtual Machine has made 
     * its best effort to recycle all unused objects. 
     * <p>
     * The name <code>gc</code> stands for "garbage 
     * collector". The Java Virtual Machine performs this recycling 
     * process automatically as needed even if the <code>gc</code> method 
     * is not invoked explicitly. 
     *
     * @since   JDK1.0
     */
    public native void gc();

    /**
     * Runs the finalization methods of any objects pending finalization.
     * Calling this method suggests that the Java Virtual Machine expend 
     * effort toward running the <code>finalize</code> methods of objects 
     * that have been found to be discarded but whose <code>finalize</code> 
     * methods have not yet been run. When control returns from the 
     * method call, the Java Virtual Machine has made a best effort to 
     * complete all outstanding finalizations. 
     * <p>
     * The Java Virtual Machine performs the finalization process 
     * automatically as needed if the <code>runFinalization</code> method 
     * is not invoked explicitly. 
     *
     * @see     java.lang.Object#finalize()
     * @since   JDK1.0
     */
    public native void runFinalization();

    /**
     * Enables/Disables tracing of instructions.
     * If the <code>boolean</code> argument is <code>true</code>, this 
     * method asks the Java Virtual Machine to print out a detailed trace 
     * of each instruction in the Java Virtual Machine as it is executed. 
     * The virtual machine may ignore this request if it does not support 
     * this feature. The destination of the trace output is system 
     * dependent. 
     * <p>
     * If the <code>boolean</code> argument is <code>false</code>, this 
     * method causes the Java Virtual Machine to stop performing the 
     * detailed instruction trace it is performing. 
     *
     * @param   on   <code>true</code> to enable instruction tracing;
     *               <code>false</code> to disable this feature.
     * @since   JDK1.0
     */
    public native void traceInstructions(boolean on);

    /**
     * Enables/Disables tracing of method calls.
     * If the <code>boolean</code> argument is <code>true</code>, this 
     * method asks the Java Virtual Machine to print out a detailed trace 
     * of each method in the Java Virtual Machine as it is called. The 
     * virtual machine may ignore this request if it does not support 
     * this feature. The destination of the trace output is system dependent. 
     * <p>
     * If the <code>boolean</code> argument is <code>false</code>, this 
     * method causes the Java Virtual Machine to stop performing the 
     * detailed method trace it is performing. 
     *
     * @param   on   <code>true</code> to enable instruction tracing;
     *               <code>false</code> to disable this feature.
     * @since   JDK1.0
     */
    public native void traceMethodCalls(boolean on);

    /**
     * Initializes the linker and returns the search path for shared libraries.
     */
    private synchronized native String initializeLinkerInternal();
    private native String buildLibName(String pathname, String filename);

    /* Helper for load and loadLibrary */
    private native int loadFileInternal(String filename);

    /** The paths searched for libraries */
    private String paths[];

    private void initializeLinker() {
	String ldpath = initializeLinkerInternal();
	char c = System.getProperty("path.separator").charAt(0);
	int ldlen = ldpath.length();
	int i, j, n;
	// Count the separators in the path
	i = ldpath.indexOf(c);
	n = 0;
	while (i >= 0) {
	    n++;
	    i = ldpath.indexOf(c, i+1);
	}

	// allocate the array of paths - n :'s = n + 1 path elements
	paths = new String[n + 1];

	// Fill the array with paths from the ldpath
	n = i = 0;
	j = ldpath.indexOf(c);
	while (j >= 0) {
	    if (j - i > 0) {
		paths[n++] = ldpath.substring(i, j);
	    } else if (j - i == 0) { 
		paths[n++] = ".";
	    }
	    i = j + 1;
	    j = ldpath.indexOf(c, i);
	}
	paths[n] = ldpath.substring(i, ldlen);
    }

    /**
     * Loads the specified filename as a dynamic library. The filename 
     * argument must be a complete pathname. 
     * From <code>java_g</code> it will automagically insert "_g" before the
     * ".so" (for example
     * <code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).
     * <p>
     * If there is a security manager, its <code>checkLink</code> method 
     * is called with the <code>filename</code> as its argument. This may 
     * result in a security exception. 
     *
     * @param      filename   the file to load.
     * @exception  SecurityException     if the current thread cannot load the
     *               specified dynamic library.
     * @exception  UnsatisfiedLinkError  if the file does not exist.
     * @see        java.lang.Runtime#getRuntime()
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkLink(java.lang.String)
     * @since      JDK1.0
     */
    public synchronized void load(String filename) {
	SecurityManager security = System.getSecurityManager();
	int ret;
	if (security != null) {
	    security.checkLink(filename);
	}
	ret = loadFileInternal(filename);
	if (ret == -1) {
	    throw new OutOfMemoryError();
	} else if (ret == 0) {
	    throw new UnsatisfiedLinkError(filename);
	}   /* else load was successful; return */
    }

    /**
     * Loads the dynamic library with the specified library name. The 
     * mapping from a library name to a specific filename is done in a 
     * system-specific manner. 
     * <p>
     * First, if there is a security manager, its <code>checkLink</code> 
     * method is called with the <code>filename</code> as its argument. 
     * This may result in a security exception. 
     * <p>
     * If this method is called more than once with the same library 
     * name, the second and subsequent calls are ignored. 
     *
     * @param      libname   the name of the library.
     * @exception  SecurityException     if the current thread cannot load the
     *               specified dynamic library.
     * @exception  UnsatisfiedLinkError  if the library does not exist.
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkLink(java.lang.String)
     * @since      JDK1.0
     */
    public synchronized void loadLibrary(String libname) {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkLink(libname);
	}
        if (paths == null) {
            initializeLinker();
	}
	for (int i = 0 ; i < paths.length ; i++) {
	    int ret;
	    String tempname = buildLibName(paths[i], libname);
	    ret = loadFileInternal(tempname);
	    if (ret == -1) {
		throw new OutOfMemoryError();
	    } else if (ret == 1) {	// Loaded or found it already loaded
		return;
	    }
	}
	// Oops, it failed
        throw new UnsatisfiedLinkError("no " + libname + 
					   " in shared library path");
    }

    /**
     * Creates a localized version of an input stream. This method takes 
     * an <code>InputStream</code> and returns an <code>InputStream</code> 
     * equivalent to the argument in all respects except that it is 
     * localized: as characters in the local character set are read from 
     * the stream, they are automatically converted from the local 
     * character set to Unicode. 
     * <p>
     * If the argument is already a localized stream, it may be returned 
     * as the result. 
     *
     * @deprecated As of JDK&nbsp;1.1, the preferred way translate a byte
     * stream in the local encoding into a character stream in Unicode is via
     * the <code>InputStreamReader</code> and <code>BufferedReader</code>
     * classes.
     *
     * @return     a localized input stream.
     * @see        java.io.InputStream
     * @see        java.io.BufferedReader#BufferedReader(java.io.Reader)
     * @see        java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
     */
    public InputStream getLocalizedInputStream(InputStream in) {
	return in;
    }

    /**
     * Creates a localized version of an output stream. This method 
     * takes an <code>OutputStream</code> and returns an 
     * <code>OutputStream</code> equivalent to the argument in all respects 
     * except that it is localized: as Unicode characters are written to 
     * the stream, they are automatically converted to the local 
     * character set. 
     * <p>
     * If the argument is already a localized stream, it may be returned 
     * as the result. 
     *
     * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a
     * Unicode character stream into a byte stream in the local encoding is via
     * the <code>OutputStreamWriter</code>, <code>BufferedWriter</code>, and
     * <code>PrintWriter</code> classes.
     *
     * @return     a localized output stream.
     * @see        java.io.OutputStream
     * @see        java.io.BufferedWriter#BufferedWriter(java.io.Writer)
     * @see        java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
     * @see        java.io.PrintWriter#PrintWriter(java.io.OutputStream)
     */
    public OutputStream getLocalizedOutputStream(OutputStream out) {
	return out;
    }

}