java.io.FileDescriptor Maven / Gradle / Ivy
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.io;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Instances of the file descriptor class serve as an opaque handle
* to the underlying machine-specific structure representing an open
* file, an open socket, or another source or sink of bytes. The
* main practical use for a file descriptor is to create a
* FileInputStream or FileOutputStream to
* contain it.
*
* Applications should not create their own file descriptors.
*
* @author Pavani Diwanji
* @see java.io.FileInputStream
* @see java.io.FileOutputStream
* @since JDK1.0
*/
public final class FileDescriptor {
private int fd;
/**
* A counter for tracking the FIS/FOS/RAF instances that
* use this FileDescriptor. The FIS/FOS.finalize() will not release
* the FileDescriptor if it is still under user by a stream.
*/
private AtomicInteger useCount;
/**
* Constructs an (invalid) FileDescriptor
* object.
*/
public /**/ FileDescriptor() {
fd = -1;
useCount = new AtomicInteger();
}
private /* */ FileDescriptor(int fd) {
this.fd = fd;
useCount = new AtomicInteger();
}
/**
* A handle to the standard input stream. Usually, this file
* descriptor is not used directly, but rather via the input stream
* known as System.in.
*
* @see java.lang.System#in
*/
public static final FileDescriptor in = new FileDescriptor(0);
/**
* A handle to the standard output stream. Usually, this file
* descriptor is not used directly, but rather via the output stream
* known as System.out.
* @see java.lang.System#out
*/
public static final FileDescriptor out = new FileDescriptor(1);
/**
* A handle to the standard error stream. Usually, this file
* descriptor is not used directly, but rather via the output stream
* known as System.err.
*
* @see java.lang.System#err
*/
public static final FileDescriptor err = new FileDescriptor(2);
/**
* Tests if this file descriptor object is valid.
*
* @return true if the file descriptor object represents a
* valid, open file, socket, or other active I/O connection;
* false otherwise.
*/
public boolean valid() {
return fd != -1;
}
/**
* Force all system buffers to synchronize with the underlying
* device. This method returns after all modified data and
* attributes of this FileDescriptor have been written to the
* relevant device(s). In particular, if this FileDescriptor
* refers to a physical storage medium, such as a file in a file
* system, sync will not return until all in-memory modified copies
* of buffers associated with this FileDescriptor have been
* written to the physical medium.
*
* sync is meant to be used by code that requires physical
* storage (such as a file) to be in a known state For
* example, a class that provided a simple transaction facility
* might use sync to ensure that all changes to a file caused
* by a given transaction were recorded on a storage medium.
*
* sync only affects buffers downstream of this FileDescriptor. If
* any in-memory buffering is being done by the application (for
* example, by a BufferedOutputStream object), those buffers must
* be flushed into the FileDescriptor (for example, by invoking
* OutputStream.flush) before that data will be affected by sync.
*
* @exception SyncFailedException
* Thrown when the buffers cannot be flushed,
* or because the system cannot guarantee that all the
* buffers have been synchronized with physical media.
* @since JDK1.1
*/
public native void sync() throws SyncFailedException;
// package private methods used by FIS, FOS and RAF
int incrementAndGetUseCount() {
return useCount.incrementAndGet();
}
int decrementAndGetUseCount() {
return useCount.decrementAndGet();
}
}