Reference:Android.os.IBinder
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android.os
public interface android.os.IBinder
| android.os.IBinder |
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 Binder.
The key IBinder API is transact() matched by 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 transact() does not return until the target has returned from 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.
The data sent through transact() is a 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.
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.
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.
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:
- The transact() method will throw a DeadObjectException exception if you try to call it on an IBinder whose process no longer exists.
- The pingBinder() method can be called, and will return false if the remote process no longer exists.
- The linkToDeath() method can be used to register a IBinder.DeathRecipient with the IBinder, which will be called when its containing process goes away.
[edit] Nested Classes
IBinder.DeathRecipient Interface for receiving a callback when the process hosting an IBinder has gone away. [edit] Known Indirect Subclasses
Binder, BluetoothServiceNative, IChatListener.Stub, IChatSession.Stub, IGTalkService.Stub, IGTalkSession.Stub, IGroupChatInvitationListener.Stub, IPhone.Stub, IRosterListener.Stub, ISimPhoneBook.Stub, ISms.Stub, ISyncObserver.Stub, IUsb.Stub, SimPhoneBookInterfaceManager, SimSmsInterfaceManager, SyncContextTest.IPC.T
See Also
[edit] Summary
[edit] Constants
Value int DUMP_TRANSACTION IBinder protocol transaction code: dump internal state. 1598311760 0x5f444d50 int FIRST_CALL_TRANSACTION The first transaction code available for user commands. 1 0x00000001 int LAST_CALL_TRANSACTION The last transaction code available for user commands. 16777215 0x00ffffff int PING_TRANSACTION IBinder protocol transaction code: pingBinder(). 1599098439 0x5f504e47 [edit] Public Methods
int getConstantData (Parcel outData) This method allows you to add data that is transported through IPC along with your IBinder pointer. void linkToDeath (DeathRecipient recipient, int flags) Register the recipient for a notification if this binder goes away. boolean pingBinder () Check to see if the object still exists. IInterface queryLocalInterface (String descriptor) Attempt to retrieve a local implementation of an interface for this Binder object. boolean transact (int code, Parcel data, Parcel reply, int flags) Perform a generic operation with the object. boolean unlinkToDeath (DeathRecipient recipient, int flags) Remove a previously registered death notification. [edit] Details
[edit] Constants
[edit] public static final int DUMP_TRANSACTION
IBinder protocol transaction code: dump internal state. Constant Value: 1598311760 (0x5f444d50)
[edit] public static final int FIRST_CALL_TRANSACTION
The first transaction code available for user commands. Constant Value: 1 (0x00000001)
[edit] public static final int LAST_CALL_TRANSACTION
The last transaction code available for user commands. Constant Value: 16777215 (0x00ffffff)
[edit] public static final int PING_TRANSACTION
IBinder protocol transaction code: pingBinder(). Constant Value: 1599098439 (0x5f504e47)
[edit] Public Methods
[edit] public int getConstantData(Parcel outData)
This method allows you to add data that is transported through IPC along with your IBinder pointer. When implementing a Binder object, override it to write your desired data in to outData. You can then call getConstantData() on your IBinder to retrieve that data, from any process. You MUST return the number of bytes written in to the parcel (including padding).
[edit] public void linkToDeath(DeathRecipient recipient, int flags)
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 IBinder.DeathRecipient 's DeathRecipient.binderDied() method will be called.
You will only receive death notifications for remote binders, as local binders by definition can't die without you dying as well.
Throws
DeadObjectException if the target IBinder's process has already died. DeadObjectException See Also
[edit] public boolean pingBinder()
Check to see if the object still exists.
Returns
- Returns false if the hosting process is gone, otherwise the result (always by default true) returned by the pingBinder() implementation on the other side.
[edit] public IInterface queryLocalInterface(String descriptor)
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.
[edit] public boolean transact(int code, Parcel data, Parcel reply, int flags)
Perform a generic operation with the object. The code should be a number between FIRST_CALL_TRANSACTION and LAST_CALL_TRANSACTION, data is the data being sent to the object, reply will be filled in with its result, and flags should always be zero.
Throws
DeadObjectException [edit] public boolean unlinkToDeath(DeathRecipient recipient, int flags)
Remove a previously registered death notification. The recipient will no longer be called if this object dies.
Returns
- Returns true if the recipient is successfully unlinked, assuring you that its 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
NoSuchElementException if the givenrecipient has not been registered with the IBinder, and the IBinder is still alive. Note that if the recipientwas never registered, but the IBinder has already died, then this exception will not be thrown, and you will receive a false return value instead. [edit] References
- Original documentation page for Android SDK build m5-rc15e - 14 apr 2008 17:27
