/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import java.io.FileDescriptor;
import java.io.PrintWriter;
/**
* Base interface for a remotable object, the core part of a lightweight
* remote procedure call mechanism designed for high performance when
* performing in-process and cross-process calls. This
* interface describes the abstract protocol for interacting with a
* remotable object. Do not implement this interface directly, instead
* extend from {@link Binder}.
*
* <p>The key IBinder API is {@link #transact transact()} matched by
* {@link Binder#onTransact Binder.onTransact()}. These
* methods allow you to send a call to an IBinder object and receive a
* call coming in to a Binder object, respectively. This transaction API
* is synchronous, such that a call to {@link #transact transact()} does not
* return until the target has returned from
* {@link Binder#onTransact Binder.onTransact()}; this is the
* expected behavior when calling an object that exists in the local
* process, and the underlying inter-process communication (IPC) mechanism
* ensures that these same semantics apply when going across processes.
*
* <p>The data sent through transact() is a {@link Parcel}, a generic buffer
* of data that also maintains some meta-data about its contents. The meta
* data is used to manage IBinder object references in the buffer, so that those
* references can be maintained as the buffer moves across processes. This
* mechanism ensures that when an IBinder is written into a Parcel and sent to
* another process, if that other process sends a reference to that same IBinder
* back to the original process, then the original process will receive the
* same IBinder object back. These semantics allow IBinder/Binder objects to
* be used as a unique identity (to serve as a token or for other purposes)
* that can be managed across processes.
*
* <p>The system maintains a pool of transaction threads in each process that
* it runs in. These threads are used to dispatch all
* IPCs coming in from other processes. For example, when an IPC is made from
* process A to process B, the calling thread in A blocks in transact() as
* it sends the transaction to process B. The next available pool thread in
* B receives the incoming transaction, calls Binder.onTransact() on the target
* object, and replies with the result Parcel. Upon receiving its result, the
* thread in process A returns to allow its execution to continue. In effect,
* other processes appear to use as additional threads that you did not create
* executing in your own process.
*
* <p>The Binder system also supports recursion across processes. For example
* if process A performs a transaction to process B, and process B while
* handling that transaction calls transact() on an IBinder that is implemented
* in A, then the thread in A that is currently waiting for the original
* transaction to finish will take care of calling Binder.onTransact() on the
* object being called by B. This ensures that the recursion semantics when
* calling remote binder object are the same as when calling local objects.
*
* <p>When working with remote objects, you often want to find out when they
* are no longer valid. There are three ways this can be determined:
* <ul>
* <li> The {@link #transact transact()} method will throw a
* {@link RemoteException} exception if you try to call it on an IBinder
* whose process no longer exists.
* <li> The {@link #pingBinder()} method can be called, and will return false
* if the remote process no longer exists.
* <li> The {@link #linkToDeath linkToDeath()} method can be used to register
* a {@link DeathRecipient} with the IBinder, which will be called when its
* containing process goes away.
* </ul>
*
* @see Binder
*/
public interface IBinder {
/**
* The first transaction code available for user commands.
*/
int FIRST_CALL_TRANSACTION = 0x00000001;
/**
* The last transaction code available for user commands.
*/
int LAST_CALL_TRANSACTION = 0x00ffffff;
/**
* IBinder protocol transaction code: pingBinder().
*/
int PING_TRANSACTION = ('_'<<24)|('P'<<16)|('N'<<8)|'G';
/**
* IBinder protocol transaction code: dump internal state.
*/
int DUMP_TRANSACTION = ('_'<<24)|('D'<<16)|('M'<<8)|'P';
/**
* IBinder protocol transaction code: interrogate the recipient side
* of the transaction for its canonical interface descriptor.
*/
int INTERFACE_TRANSACTION = ('_'<<24)|('N'<<16)|('T'<<8)|'F';
/**
* Flag to {@link #transact}: this is a one-way call, meaning that the
* caller returns immediately, without waiting for a result from the
* callee. Applies only if the caller and callee are in different
* processes.
*/
int FLAG_ONEWAY = 0x00000001;
/**
* Get the canonical name of the interface supported by this binder.
*/
public String getInterfaceDescriptor() throws RemoteException;
/**
* Check to see if the object still exists.
*
* @return Returns false if the
* hosting process is gone, otherwise the result (always by default
* true) returned by the pingBinder() implementation on the other
* side.
*/
public boolean pingBinder();
/**
* Check to see if the process that the binder is in is still alive.
*
* @return false if the process is not alive. Note that if it returns
* true, the process may have died while the call is returning.
*/
public boolean isBinderAlive();
/**
* Attempt to retrieve a local implementation of an interface
* for this Binder object. If null is returned, you will need
* to instantiate a proxy class to marshall calls through
* the transact() method.
*/
public IInterface queryLocalInterface(String descriptor);
/**
* Print the object's state into the given stream.
*
* @param fd The raw file descriptor that the dump is being sent to.
* @param args additional arguments to the dump request.
*/
public void dump(FileDescriptor fd, String[] args) throws RemoteException;
/**
* Perform a generic operation with the object.
*
* @param code The action to perform. This should
* be a number between {@link #FIRST_CALL_TRANSACTION} and
* {@link #LAST_CALL_TRANSACTION}.
* @param data Marshalled data to send to the target. Most not be null.
* If you are not sending any data, you must create an empty Parcel
* that is given here.
* @param reply Marshalled data to be received from the target. May be
* null if you are not interested in the return value.
* @param flags Additional operation flags. Either 0 for a normal
* RPC, or {@link #FLAG_ONEWAY} for a one-way RPC.
*/
public boolean transact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException;
/**
* Interface for receiving a callback when the process hosting an IBinder
* has gone away.
*
* @see #linkToDeath
*/
public interface DeathRecipient {
public void binderDied();
}
/**
* Register the recipient for a notification if this binder
* goes away. If this binder object unexpectedly goes away
* (typically because its hosting process has been killed),
* then the given {@link DeathRecipient}'s
* {@link DeathRecipient#binderDied DeathRecipient.binderDied()} method
* will be called.
*
* <p>You will only receive death notifications for remote binders,
* as local binders by definition can't die without you dying as well.
*
* @throws Throws {@link RemoteException} if the target IBinder's
* process has already died.
*
* @see #unlinkToDeath
*/
public void linkToDeath(DeathRecipient recipient, int flags)
throws RemoteException;
/**
* Remove a previously registered death notification.
* The recipient will no longer be called if this object
* dies.
*
* @return Returns true if the <var>recipient</var> is successfully
* unlinked, assuring you that its
* {@link DeathRecipient#binderDied DeathRecipient.binderDied()} method
* will not be called. Returns false if the target IBinder has already
* died, meaning the method has been (or soon will be) called.
*
* @throws Throws {@link java.util.NoSuchElementException} if the given
* <var>recipient</var> has not been registered with the IBinder, and
* the IBinder is still alive. Note that if the <var>recipient</var>
* was never registered, but the IBinder has already died, then this
* exception will <em>not</em> be thrown, and you will receive a false
* return value instead.
*/
public boolean unlinkToDeath(DeathRecipient recipient, int flags);
}
