vmintegration.texinfo

linux下建立JAVA虚拟机的源码KAFFE

methods, handling integers, longs and Objects, but the field is always
changed on a put.  Different methods are provided for different semantics.
Ordered variants perform a lazy put, in that the change does not
immediately propogate to other threads, while the others provide
volatile or 'normal' semantics.
@item @code{arrayBaseOffset(Class)} and @code{arrayIndexScale(Class)} --
These two methods allow an array class to be traversed by pointer
arithmetic, by gaining the address of the first element and then
scaling appropriately for the later ones.
@item @code{park(boolean,long)} and @code{unpark(Thread)} -- These methods
block and unblock threads respectively, with an optional timeout being
provided for the blocking.  @code{unpark} is unsafe as the thread may have
been destroyed by native code. 
@end itemize

@node java.util, java.io, gnu.classpath, Classpath Hooks
@section java.util

The @code{java.util} VM hooks provide links between the mix of functionality
present in that package, which includes collections, date and time handling
and parsing.  At present, there is only one hook, which connects GNU Classpath
to the timezone information provided by the underlying platform.

@menu
* java.util.VMTimeZone::
@end menu

@node java.util.VMTimeZone,,java.util,java.util
@subsection @code{java.util.VMTimeZone}

@code{VMTimeZone} joins @code{TimeZone} to the platform timezone information
via the static method, @code{getDefaultTimeZoneId()}.  The VM hook is
expected to return a @code{TimeZone} instance that represents the current
timezone in use by the platform.  The default implementation provides
this functionality for POSIX or GNU-like systems, and VMs that want this
functionality can keep this implementation and implement the native
method, @code{getSystemTimeZoneId()}.  This method is only called when
obtaining the timezone name from the @code{TZ} environment variable,
@code{/etc/timezone} and @code{/etc/localtime} all fail.  This fallback
mechanism also means that a system which doesn't provide the above three
methods, but does provide a timezone in string form, can still use this
implementation.

@node java.io, java.security, java.util, Classpath Hooks
@section java.io

The @code{java.io} package is heavily reliant on access to the I/O facilities
of the underlying platform.  As far as its VM hooks go, they provide two
areas of functionality to GNU Classpath, these being

@itemize @bullet
@item File and directory queries and manipulation
@item Serialization of objects
@end itemize

The first corresponds directly to most of the @code{File} class, while
the latter underlies the functionality provided by the
@code{ObjectInputStream} and @code{ObjectOutputStream}.  More low-level I/O
is provided by @ref{java.nio}.

@menu
* java.io.VMFile::
* java.io.VMObjectInputStream::
* java.io.VMObjectStreamClass::
@end menu

@node java.io.VMFile,java.io.VMObjectInputStream,java.io,java.io
@subsection @code{java.io.VMFile}

@code{VMFile} allows GNU Classpath's @code{File} representations to
probe and modify the file system using the native functions of the
platform.  The default implementation (which consists of both a
@code{VMFile} class and the native methods) is primarily UNIX-centric,
working with POSIX functions and assuming case-sensitive filenames,
without the restriction of the 8.3 format.  It consists mainly of
@code{static} @code{native} methods, with a few Java helper methods.
The native methods represent the file as a string containing its path,
rather than using the object itself.

@itemize @bullet
@item Native Methods
@itemize @bullet
@item @code{lastModified(String)} -- The native method should return a
@code{long} value that represents the last modified date of the file.
@item @code{setReadOnly(String)} -- Sets the file's permissions to read only,
in whichever way this is realised by the platform.
@item @code{create(String)} -- Create the named file.
@item @code{list(String)} -- The native method opens the named directory,
reads the contents and returns them as a Java @code{String} array.
@item @code{renameTo(String,String)} -- Renames the first file to the second.
@item @code{length(String)} -- Returns a @code{long} value representing
the file size.
@item @code{exists(String)} -- Tests for the existence of the named file
or directory.
@item @code{delete(String)} -- Deletes the file or directory.
@item @code{setLastModified(String,long)} -- Change the last modified time.
@item @code{mkdir(String)} -- Creates the named directory.
@item @code{isFile(String)} -- Tests that the named path references a file.
@item @code{canWrite(String)} -- Tests that the file can be written to.
This method is @code{synchronized}, so the object is locked during the check.
@item @code{canRead(String)} -- Complement of the last method.
@item @code{isDirectory(String)} -- Tests that the named path references
a directory.
@end itemize
@item Java Helper Methods
@itemize @bullet
@item @code{canWriteDirectory(File)} -- Checks that the directory can be
written to, by trying to create a temporary file in it.
@item @code{listRoots()} -- Returns the root of a GNU filesystem i.e. `/'
in an array.
@item @code{isHidden(String)} -- Checks whether the file starts with `.',
which is how files are hidden on UNIX-style systems.
@item @code{getName(String)} -- Pulls the actual filename from the end of
the path, by breaking off the characters after the last occurrence of the
platform's file separator.
@item @code{getCanonicalForm(String)} -- This converts a UNIX path to
its canonical form by removing the `.' and `..' sections that occur within.
@end itemize
@end itemize

@node java.io.VMObjectInputStream,java.io.VMObjectStreamClass,java.io.VMFile,java.io
@subsection @code{java.io.VMObjectInputStream}

This class consists of two methods which provide functionality used in
deserializing an object.  @code{currentClassLoader()} provides the first
user-defined class loader from the class context
(@xref{gnu.classpath.VMStackWalker},) via a @code{PrivilegedAction}.
@code{allocateObject(Class,Class,Constructor)} is a @code{native} method
(a reference implementation is provided) which creates an object but
calls the constructor of another class, which is a superclass of the
object's class.

@node java.io.VMObjectStreamClass,,java.io.VMObjectInputStream,java.io
@subsection @code{java.io.VMObjectStreamClass}

@code{VMObjectStreamClass} is a series of @code{static} @code{native}
methods that provide some of the groundwork for @code{ObjectStreamClass}
and @code{ObjectStreamField}.  @code{hasClassInitializer(Class)} works
with the former, and checks for the presence of a static initializer.
The remaining methods are of the form @code{setXXXNative(Field,Object,XXX)}
and support @code{ObjectStreamField}.  One exists for each of the main types
(boolean, float, double, long, int, short, char, byte and object) and is used
to set the specified field in the supplied instance to the given value.

A default implementation is provided for all of them, so a VM implementation
is optional.

@node java.security, java.net, java.io, Classpath Hooks
@section java.security

The @code{java.security} package provides support for Java's security
architecture.  At present, @code{VMAccessController} represents the sole
VM hook for this.

@menu
* java.security.VMAccessController::
@end menu

@node java.security.VMAccessController,,java.security,java.security
@subsection @code{java.security.VMAccessController}

The @code{AccessController} is used to perform privileged actions.  Its
hook class, @code{VMAccessController}, maintains the
@code{AccessControlContext} and the default implementation is purely
Java-based.  The VM may choose to replace this with their own.
The methods in the reference version are as follows:

@itemize @bullet
@item @code{pushContext(AccessControlContext)} -- Adds a new context to the
stack for the current thread.  This is called before a privileged action
takes place.
@item @code{popContext()} -- Removes the top context from the stack.  This
is performed after the privileged action takes place.
@item @code{getContext()} -- Either derives a context based on the 
@code{ProtectionDomain}s of the call stack (see the next method) or returns
the top of the context stack.
@item @code{getStack()} -- Provides access to the call stack as a pair of
arrays of classes and method names.  The actual implementation returns
an empty array, indicating that there are no permissions.
@end itemize

@node java.net, java.nio, java.security, Classpath Hooks
@section java.net

The @code{java.net} package is heavily reliant on access to the networking
facilities of the underlying platform.  The VM hooks provide information
about the available network interfaces, and access to lookup facilities
for network addresses.

@menu
* java.net.VMInetAddress::
* java.net.VMNetworkInterface::
@end menu

@node java.net.VMInetAddress,java.net.VMNetworkInterface,java.net,java.net
@subsection @code{java.net.VMInetAddress}

@code{VMInetAddress} is a series of @code{static} @code{native} methods
which provide access to the platform's lookup facilities.  All the methods
are implemented by GNU Classpath, making VM implementation optional, and
are as follows:

@itemize @bullet
@item @code{getLocalHostname()} -- Wraps the @code{gethostname} function, and
falls back on `localhost'.
@item @code{lookupInaddrAny()} -- Returns the value of @code{INADDR_ANY}.
@item @code{getHostByAddr(byte[])} -- Looks up the hostname based on an IP
address.
@item @code{getHostByName(String)} -- The reverse of the last method, it
returns the IP addresses which the given host name resolves to.
@end itemize

@node java.net.VMNetworkInterface,,java.net.VMInetAddress,java.net
@subsection @code{java.net.VMNetworkInterface}

@code{VMNetworkInterface} currently consists of a single @code{static}
@code{native} method, @code{getInterfaces()}, which retrieves the
network interfaces available on the underlying platform as a @code{Vector}.
The current GNU Classpath implementation is a native stub.

@node java.nio, java.nio.channels, java.net, Classpath Hooks
@section java.nio

The @code{java.nio} package is part of the New I/O framework added in
Java 1.4.  This splits I/O into the concepts of @emph{buffers},
@emph{charsets}, @emph{channels} and @emph{selectors}, and
@code{java.nio} defines the buffer classes.  As far as native and VM
code is concerned, the new package needs support for low-level efficient
buffer operations.

@menu
* java.nio.VMDirectByteBuffer::
@end menu

@node java.nio.VMDirectByteBuffer,,java.nio,java.nio
@subsection @code{java.nio.VMDirectByteBuffer}

A @code{ByteBuffer} maintains a buffer of bytes, and allows it to be
manipulated using primitive operations such as @code{get}, @code{put},
@code{allocate} and @code{free}.  A direct buffer avoids intermediate
copying, and uses native data which shouldn't be manipulated by a
garbage collector.  The VM class consists of @code{static} @code{native}
methods, all of which are given default implementations by GNU
Classpath.

@itemize @bullet
@item @code{init()} -- Creates an instance of an appropriate
@code{gnu.classpath.RawData} class.  This class is not garbage
collected, is created natively and is used in the other methods to reference
the buffered data.
@item @code{allocate(int)} -- Allocates the memory for the buffer using
@code{malloc} and returns a reference to the @code{RawData} class.
@item @code{free(RawData)} -- Frees the memory used by the buffer.
@item @code{get(RawData,int)}  -- Returns the data at the specified index.
@item @code{get(RawData,int,byte[],int,int)} -- Copies a section of the
data into a byte array using @code{memcpy}.
@item @code{put(RawData,int,byte)} -- Puts the given data in the buffer
at the specified index.
@item @code{adjustAddress(RawData,int)} -- Adjusts the pointer into the buffer.
@item @code{shiftDown(RawData,int,int,int)} -- Moves the content of the buffer
at an offset down to a new offset using @code{memmove}.
@end itemize
 
@node java.nio.channels, gnu.java.nio, java.nio, Classpath Hooks
@section java.nio.channels

Channels provide the data for the buffers with the New I/O packages.
For example, a channel may wrap a file or a socket.  The VM hooks,
at the moment, simply allow the channels to be accessed by @code{java.io}
streams.

@menu
* java.nio.channels.VMChannels::
@end menu

@node java.nio.channels.VMChannels,,java.nio.channels,java.nio.channels
@subsection @code{java.nio.channels.VMChannels}

@code{VMChannels} provides the methods that create the channels or
streams.  The default implementation is in pure Java and simply wraps
the channels in standard I/O classes from @code{java.io}.

@itemize @bullet
@item @code{createStream(Class,Channel)} -- Creates a @code{FileChannel}
which wraps an instance of the specified stream class, created by reflection.