runFinalization() may want to look at this to see if ALL
* finalizers should be run, because the virtual machine is about to halt.
*/
private Thread exitSequence;
/**
* All shutdown hooks. This is initialized lazily, and set to null once all
* shutdown hooks have run. Access to this field must be thread-safe; lock
* on libpath to avoid deadlock with user code.
*/
private Set shutdownHooks;
/** True if we should finalize on exit. */
private boolean finalizeOnExit;
/**
* The one and only runtime instance.
*/
private static final Runtime current = new Runtime();
/**
* Not instantiable by a user, this should only create one instance.
*/
private Runtime()
{
if (current != null)
throw new InternalError("Attempt to recreate Runtime");
// We don't use libpath in the libgcj implementation. We still
// set it to something to allow the various synchronizations to
// work.
libpath = new String[0];
}
/**
* Get the current Runtime object for this JVM. This is necessary to access
* the many instance methods of this class.
*
* @return the current Runtime object
*/
public static Runtime getRuntime()
{
return current;
}
/**
* Exit the Java runtime. This method will either throw a SecurityException
* or it will never return. The status code is returned to the system; often
* a non-zero status code indicates an abnormal exit. Of course, there is a
* security check, checkExit(status).
*
* First, all shutdown hooks are run, in unspecified order, and
* concurrently. Next, if finalization on exit has been enabled, all pending
* finalizers are run. Finally, the system calls halt.
If this is run a second time after shutdown has already started, there
* are two actions. If shutdown hooks are still executing, it blocks
* indefinitely. Otherwise, if the status is nonzero it halts immediately;
* if it is zero, it blocks indefinitely. This is typically called by
* System.exit.
System.exit was invoked), or when the user terminates
* the virtual machine (such as by typing ^C, or logging off). There is
* a security check to add hooks,
* RuntimePermission("shutdownHooks").
*
* The hook must be an initialized, but unstarted Thread. The threads
* are run concurrently, and started in an arbitrary order; and user
* threads or daemons may still be running. Once shutdown hooks have
* started, they must all complete, or else you must use halt,
* to actually finish the shutdown sequence. Attempts to modify hooks
* after shutdown has started result in IllegalStateExceptions.
It is imperative that you code shutdown hooks defensively, as you * do not want to deadlock, and have no idea what other hooks will be * running concurrently. It is also a good idea to finish quickly, as the * virtual machine really wants to shut down!
* *There are no guarantees that such hooks will run, as there are ways * to forcibly kill a process. But in such a drastic case, shutdown hooks * would do little for you in the first place.
* * @param hook an initialized, unstarted Thread * @throws IllegalArgumentException if the hook is already registered or run * @throws IllegalStateException if the virtual machine is already in * the shutdown sequence * @throws SecurityException if permission is denied * @since 1.3 * @see #removeShutdownHook(Thread) * @see #exit(int) * @see #halt(int) */ public void addShutdownHook(Thread hook) { SecurityManager sm = SecurityManager.current; // Be thread-safe! if (sm != null) sm.checkPermission(new RuntimePermission("shutdownHooks")); if (hook.isAlive() || hook.getThreadGroup() == null) throw new IllegalArgumentException("The hook thread " + hook + " must not have been already run or started"); synchronized (libpath) { if (exitSequence != null) throw new IllegalStateException("The Virtual Machine is exiting. It is not possible anymore to add any hooks"); if (shutdownHooks == null) shutdownHooks = new HashSet(); // Lazy initialization. if (! shutdownHooks.add(hook)) throw new IllegalArgumentException(hook.toString() + " had already been inserted"); } } /** * De-register a shutdown hook. As when you registered it, there is a * security check to remove hooks, *RuntimePermission("shutdownHooks").
*
* @param hook the hook to remove
* @return true if the hook was successfully removed, false if it was not
* registered in the first place
* @throws IllegalStateException if the virtual machine is already in
* the shutdown sequence
* @throws SecurityException if permission is denied
* @since 1.3
* @see #addShutdownHook(Thread)
* @see #exit(int)
* @see #halt(int)
*/
public boolean removeShutdownHook(Thread hook)
{
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkPermission(new RuntimePermission("shutdownHooks"));
synchronized (libpath)
{
if (exitSequence != null)
throw new IllegalStateException();
if (shutdownHooks != null)
return shutdownHooks.remove(hook);
}
return false;
}
/**
* Forcibly terminate the virtual machine. This call never returns. It is
* much more severe than exit, as it bypasses all shutdown
* hooks and initializers. Use caution in calling this! Of course, there is
* a security check, checkExit(status).
*
* @param status the status to exit with
* @throws SecurityException if permission is denied
* @since 1.3
* @see #exit(int)
* @see #addShutdownHook(Thread)
*/
public void halt(int status)
{
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkExit(status);
exitInternal(status);
}
/**
* Tell the VM to run the finalize() method on every single Object before
* it exits. Note that the JVM may still exit abnormally and not perform
* this, so you still don't have a guarantee. And besides that, this is
* inherently unsafe in multi-threaded code, as it may result in deadlock
* as multiple threads compete to manipulate objects. This value defaults to
* false. There is a security check, checkExit(0).
*
* @param finalizeOnExit whether to finalize all Objects on exit
* @throws SecurityException if permission is denied
* @see #exit(int)
* @see #gc()
* @since 1.1
* @deprecated never rely on finalizers to do a clean, thread-safe,
* mop-up from your code
*/
public static void runFinalizersOnExit(boolean finalizeOnExit)
{
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkExit(0);
current.finalizeOnExit = finalizeOnExit;
}
/**
* Create a new subprocess with the specified command line. Calls
* exec(cmdline, null, null). A security check is performed,
* checkExec.
*
* @param cmdline the command to call
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmdline is null
* @throws IndexOutOfBoundsException if cmdline is ""
*/
public Process exec(String cmdline) throws IOException
{
return exec(cmdline, null, null);
}
/**
* Create a new subprocess with the specified command line and environment.
* If the environment is null, the process inherits the environment of
* this process. Calls exec(cmdline, env, null). A security
* check is performed, checkExec.
*
* @param cmdline the command to call
* @param env the environment to use, in the format name=value
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmdline is null, or env has null entries
* @throws IndexOutOfBoundsException if cmdline is ""
*/
public Process exec(String cmdline, String[] env) throws IOException
{
return exec(cmdline, env, null);
}
/**
* Create a new subprocess with the specified command line, environment, and
* working directory. If the environment is null, the process inherits the
* environment of this process. If the directory is null, the process uses
* the current working directory. This splits cmdline into an array, using
* the default StringTokenizer, then calls
* exec(cmdArray, env, dir). A security check is performed,
* checkExec.
*
* @param cmdline the command to call
* @param env the environment to use, in the format name=value
* @param dir the working directory to use
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmdline is null, or env has null entries
* @throws IndexOutOfBoundsException if cmdline is ""
* @since 1.3
*/
public Process exec(String cmdline, String[] env, File dir)
throws IOException
{
StringTokenizer t = new StringTokenizer(cmdline);
String[] cmd = new String[t.countTokens()];
for (int i = 0; i < cmd.length; i++)
cmd[i] = t.nextToken();
return exec(cmd, env, dir);
}
/**
* Create a new subprocess with the specified command line, already
* tokenized. Calls exec(cmd, null, null). A security check
* is performed, checkExec.
*
* @param cmd the command to call
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmd is null, or has null entries
* @throws IndexOutOfBoundsException if cmd is length 0
*/
public Process exec(String[] cmd) throws IOException
{
return exec(cmd, null, null);
}
/**
* Create a new subprocess with the specified command line, already
* tokenized, and specified environment. If the environment is null, the
* process inherits the environment of this process. Calls
* exec(cmd, env, null). A security check is performed,
* checkExec.
*
* @param cmd the command to call
* @param env the environment to use, in the format name=value
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmd is null, or cmd or env has null
* entries
* @throws IndexOutOfBoundsException if cmd is length 0
*/
public Process exec(String[] cmd, String[] env) throws IOException
{
return exec(cmd, env, null);
}
/**
* Create a new subprocess with the specified command line, already
* tokenized, and the specified environment and working directory. If the
* environment is null, the process inherits the environment of this
* process. If the directory is null, the process uses the current working
* directory. A security check is performed, checkExec.
*
* @param cmd the command to call
* @param env the environment to use, in the format name=value
* @param dir the working directory to use
* @return the Process object
* @throws SecurityException if permission is denied
* @throws IOException if an I/O error occurs
* @throws NullPointerException if cmd is null, or cmd or env has null
* entries
* @throws IndexOutOfBoundsException if cmd is length 0
* @since 1.3
*/
public Process exec(String[] cmd, String[] env, File dir)
throws IOException
{
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkExec(cmd[0]);
return execInternal(cmd, env, dir);
}
/**
* Returns the number of available processors currently available to the
* virtual machine. This number may change over time; so a multi-processor
* program want to poll this to determine maximal resource usage.
*
* @return the number of processors available, at least 1
*/
public native int availableProcessors();
/**
* Find out how much memory is still free for allocating Objects on the heap.
*
* @return the number of bytes of free memory for more Objects
*/
public native long freeMemory();
/**
* Find out how much memory total is available on the heap for allocating
* Objects.
*
* @return the total number of bytes of memory for Objects
*/
public native long totalMemory();
/**
* Returns the maximum amount of memory the virtual machine can attempt to
* use. This may be Long.MAX_VALUE if there is no inherent
* limit (or if you really do have a 8 exabyte memory!).
*
* @return the maximum number of bytes the virtual machine will attempt
* to allocate
*/
public native long maxMemory();
/**
* Run the garbage collector. This method is more of a suggestion than
* anything. All this method guarantees is that the garbage collector will
* have "done its best" by the time it returns. Notice that garbage
* collection takes place even without calling this method.
*/
public native void gc();
/**
* Run finalization on all Objects that are waiting to be finalized. Again,
* a suggestion, though a stronger one than {@link #gc()}. This calls the
* finalize method of all objects waiting to be collected.
*
* @see #finalize()
*/
public native void runFinalization();
/**
* Tell the VM to trace every bytecode instruction that executes (print out
* a trace of it). No guarantees are made as to where it will be printed,
* and the VM is allowed to ignore this request.
*
* @param on whether to turn instruction tracing on
*/
public native void traceInstructions(boolean on);
/**
* Tell the VM to trace every method call that executes (print out a trace
* of it). No guarantees are made as to where it will be printed, and the
* VM is allowed to ignore this request.
*
* @param on whether to turn method tracing on
*/
public native void traceMethodCalls(boolean on);
/**
* Load a native library using the system-dependent filename. This is similar
* to loadLibrary, except the only name mangling done is inserting "_g"
* before the final ".so" if the VM was invoked by the name "java_g". There
* may be a security check, of checkLink.
*
* @param filename the file to load
* @throws SecurityException if permission is denied
* @throws UnsatisfiedLinkError if the library is not found
*/
public void load(String filename)
{
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkLink(filename);
_load(filename, false);
}
/**
* Load a native library using a system-independent "short name" for the
* library. It will be transformed to a correct filename in a
* system-dependent manner (for example, in Windows, "mylib" will be turned
* into "mylib.dll"). This is done as follows: if the context that called
* load has a ClassLoader cl, then cl.findLibrary(libpath) is
* used to convert the name. If that result was null, or there was no class
* loader, this searches each directory of the system property
* java.library.path for a file named
* System.mapLibraryName(libname). There may be a security
* check, of checkLink.
*
* @param libname the library to load
*
* @throws SecurityException if permission is denied
* @throws UnsatisfiedLinkError if the library is not found
*
* @see System#mapLibraryName(String)
* @see ClassLoader#findLibrary(String)
*/
public void loadLibrary(String libname)
{
// This is different from the Classpath implementation, but I
// believe it is more correct.
SecurityManager sm = SecurityManager.current; // Be thread-safe!
if (sm != null)
sm.checkLink(libname);
_load(libname, true);
}
/**
* Return a localized version of this InputStream, meaning all characters
* are localized before they come out the other end.
*
* @param in the stream to localize
* @return the localized stream
* @deprecated InputStreamReader is the preferred way to read
* local encodings
*/
public InputStream getLocalizedInputStream(InputStream in)
{
return in;
}
/**
* Return a localized version of this OutputStream, meaning all characters
* are localized before they are sent to the other end.
*
* @param out the stream to localize
* @return the localized stream
* @deprecated OutputStreamWriter is the preferred way to write
* local encodings
*/
public OutputStream getLocalizedOutputStream(OutputStream out)
{
return out;
}
/**
* Native method that actually shuts down the virtual machine.
*
* @param status the status to end the process with
*/
native void exitInternal(int status);
/**
* Load a file. If it has already been loaded, do nothing. The name has
* already been mapped to a true filename.
*
* @param filename the file to load
* @param do_search True if we should search the load path for the file
*/
native void _load(String filename, boolean do_search);
/**
*This is a helper function for the ClassLoader which can load
* compiled libraries. Returns true if library (which is just the
* base name -- path searching is done by this function) was loaded,
* false otherwise.
*/
native boolean loadLibraryInternal(String libname);
/**
* A helper for Runtime static initializer which does some internal native
* initialization.
*/
private static native void init ();
/**
* Run finalizers when exiting.
*/
private native void runFinalizationForExit();
/**
* Map a system-independent "short name" to the full file name, and append
* it to the path.
* XXX This method is being replaced by System.mapLibraryName.
*
* @param pathname the path
* @param libname the short version of the library name
* @return the full filename
*/
static native String nativeGetLibname(String pathname, String libname);
/**
* Execute a process. The command line has already been tokenized, and
* the environment should contain name=value mappings. If directory is null,
* use the current working directory; otherwise start the process in that
* directory.
*
* @param cmd the non-null command tokens
* @param env the non-null environment setup
* @param dir the directory to use, may be null
* @return the newly created process
* @throws NullPointerException if cmd or env have null elements
* @throws IOException if the exec fails
*/
native Process execInternal(String[] cmd, String[] env, File dir)
throws IOException;
} // class Runtime