Binder
open class Binder : IBinder
kotlin.Any | |
↳ | android.os.Binder |
Base class for a remotable object, the core part of a lightweight remote procedure call mechanism defined by IBinder
. This class is an implementation of IBinder that provides standard local implementation of such an object.
Most developers will not implement this class directly, instead using the aidl tool to describe the desired interface, having it generate the appropriate Binder subclass. You can, however, derive directly from Binder to implement your own custom RPC protocol or simply instantiate a raw Binder object directly to use as a token that can be shared across processes.
This class is just a basic IPC primitive; it has no impact on an application's lifecycle, and is valid only as long as the process that created it continues to run. To use this correctly, you must be doing so within the context of a top-level application component (a android.app.Service
, android.app.Activity
, or android.content.ContentProvider
) that lets the system know your process should remain running.
You must keep in mind the situations in which your process could go away, and thus require that you later re-create a new Binder and re-attach it when the process starts again. For example, if you are using this within an android.app.Activity
, your activity's process may be killed any time the activity is not started; if the activity is later re-created you will need to create a new Binder and hand it back to the correct place again; you need to be aware that your process may be started for another reason (for example to receive a broadcast) that will not involve re-creating the activity and thus run its code to create a new Binder.
Summary
Inherited constants | |
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Public constructors | |
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Binder() Default constructor just initializes the object. |
|
Constructor for creating a raw Binder object (token) along with a descriptor. |
Public methods | |
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open Unit |
attachInterface(owner: IInterface?, descriptor: String?) Convenience method for associating a specific interface with the Binder. |
static Long |
Reset the identity of the incoming IPC on the current thread. |
static Long |
Clears the work source on this thread. |
open Unit |
dump(fd: FileDescriptor, args: Array<String!>?) Implemented to call the more convenient version |
open Unit |
dumpAsync(fd: FileDescriptor, args: Array<String!>?) Like |
static Unit |
Flush any Binder commands pending in the current thread to the kernel driver. |
static Int |
Return the ID of the process that sent you the current transaction that is being processed. |
static Int |
Return the Linux UID assigned to the process that sent you the current transaction that is being processed. |
static Int |
Return the Linux UID assigned to the process that sent the transaction currently being processed. |
static UserHandle |
Return the UserHandle assigned to the process that sent you the current transaction that is being processed. |
static Int |
Returns the work source set by the caller. |
open String? |
Default implementation returns an empty interface name. |
open Boolean |
Check to see if the process that the binder is in is still alive. |
static Unit |
Add the calling thread to the IPC thread pool. |
open Unit |
linkToDeath(recipient: IBinder.DeathRecipient, flags: Int) Local implementation is a no-op. |
open Boolean |
Default implementation always returns true -- if you got here, the object is alive. |
open IInterface? |
queryLocalInterface(descriptor: String) Use information supplied to |
static Unit |
restoreCallingIdentity(token: Long) Restore the identity of the incoming IPC on the current thread back to a previously identity that was returned by |
static Unit |
restoreCallingWorkSource(token: Long) Restores the work source on this thread using a token returned by |
static Long |
setCallingWorkSourceUid(workSource: Int) Sets the work source for this thread. |
Boolean |
Default implementation rewinds the parcels and calls onTransact. |
open Boolean |
unlinkToDeath(recipient: IBinder.DeathRecipient, flags: Int) Local implementation is a no-op. |
Protected methods | |
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open Unit |
dump(fd: FileDescriptor, fout: PrintWriter, args: Array<String!>?) Print the object's state into the given stream. |
open Boolean |
onTransact(code: Int, data: Parcel, reply: Parcel?, flags: Int) Default implementation is a stub that returns false. |
Public constructors
Binder
Binder()
Default constructor just initializes the object.
If you're creating a Binder token (a Binder object without an attached interface), you should use Binder(java.lang.String)
instead.
Binder
Binder(descriptor: String?)
Constructor for creating a raw Binder object (token) along with a descriptor.
The descriptor of binder objects usually specifies the interface they are implementing. In case of binder tokens, no interface is implemented, and the descriptor can be used as a sort of tag to help identify the binder token. This will help identify remote references to these objects more easily when debugging.
Parameters | |
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descriptor |
String?: Used to identify the creator of this token, for example the class name. Instead of creating multiple tokens with the same descriptor, consider adding a suffix to help identify them. This value may be null . |
Public methods
attachInterface
open fun attachInterface(
owner: IInterface?,
descriptor: String?
): Unit
Convenience method for associating a specific interface with the Binder. After calling, queryLocalInterface()
will be implemented for you to return the given owner IInterface when the corresponding descriptor is requested.
Parameters | |
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owner |
IInterface?: This value may be null . |
descriptor |
String?: This value may be null . |
clearCallingIdentity
static fun clearCallingIdentity(): Long
Reset the identity of the incoming IPC on the current thread. This can be useful if, while handling an incoming call, you will be calling on interfaces of other objects that may be local to your process and need to do permission checks on the calls coming into them (so they will check the permission of your own local process, and not whatever process originally called you).
Return | |
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Long |
Returns an opaque token that can be used to restore the original calling identity by passing it to restoreCallingIdentity(long) . |
clearCallingWorkSource
static fun clearCallingWorkSource(): Long
Clears the work source on this thread.
The work source will be propagated for future outgoing binder transactions executed on this thread.
restoreCallingWorkSource(long)
must always be called after clearing the worksource.
A typical use case would be
long token = Binder.clearCallingWorkSource(); try { // Call an API. } finally { Binder.restoreCallingWorkSource(token); }
Return | |
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Long |
token to restore original work source. |
dump
open fun dump(
fd: FileDescriptor,
args: Array<String!>?
): Unit
Implemented to call the more convenient version dump(java.io.FileDescriptor,java.io.PrintWriter,java.lang.String[])
.
Parameters | |
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fd |
FileDescriptor: This value cannot be null . |
args |
Array<String!>?: This value may be null . |
dumpAsync
open fun dumpAsync(
fd: FileDescriptor,
args: Array<String!>?
): Unit
Like dump(java.io.FileDescriptor,java.lang.String[])
, but ensures the target executes asynchronously.
Parameters | |
---|---|
fd |
FileDescriptor: This value cannot be null . |
args |
Array<String!>?: This value may be null . |
flushPendingCommands
static fun flushPendingCommands(): Unit
Flush any Binder commands pending in the current thread to the kernel driver. This can be useful to call before performing an operation that may block for a long time, to ensure that any pending object references have been released in order to prevent the process from holding on to objects longer than it needs to.
getCallingPid
static fun getCallingPid(): Int
Return the ID of the process that sent you the current transaction that is being processed. This PID can be used with higher-level system services to determine its identity and check permissions. If the current thread is not currently executing an incoming transaction, then its own PID is returned. Warning: oneway transactions do not receive PID. Even if you expect a transaction to be synchronous, a misbehaving client could send it as a asynchronous call and result in a 0 PID here. Additionally, if there is a race and the calling process dies, the PID may still be 0 for a synchronous call.
getCallingUid
static fun getCallingUid(): Int
Return the Linux UID assigned to the process that sent you the current transaction that is being processed. This UID can be used with higher-level system services to determine its identity and check permissions. If the current thread is not currently executing an incoming transaction, then its own UID is returned.
getCallingUidOrThrow
static fun getCallingUidOrThrow(): Int
Return the Linux UID assigned to the process that sent the transaction currently being processed.
Exceptions | |
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java.lang.IllegalStateException |
if the current thread is not currently executing an incoming transaction and the calling identity has not been explicitly set with clearCallingIdentity() |
getCallingUserHandle
static fun getCallingUserHandle(): UserHandle
Return the UserHandle assigned to the process that sent you the current transaction that is being processed. This is the user of the caller. It is distinct from getCallingUid()
in that a particular user will have multiple distinct apps running under it each with their own UID. If the current thread is not currently executing an incoming transaction, then its own UserHandle is returned.
Return | |
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UserHandle |
This value cannot be null . |
See Also
getCallingWorkSourceUid
static fun getCallingWorkSourceUid(): Int
Returns the work source set by the caller.
Unlike getCallingUid()
, this result of this method cannot be trusted. The caller can set the value to whatever they want. Only use this value if you trust the calling UID.
Return | |
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Int |
The original UID responsible for the binder transaction. |
getInterfaceDescriptor
open fun getInterfaceDescriptor(): String?
Default implementation returns an empty interface name.
Return | |
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String? |
This value may be null . |
isBinderAlive
open fun isBinderAlive(): Boolean
Check to see if the process that the binder is in is still alive. Note that if you're calling on a local binder, this always returns true because your process is alive if you're calling it.
Return | |
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Boolean |
false if the process is not alive. Note that if it returns true, the process may have died while the call is returning. |
joinThreadPool
static fun joinThreadPool(): Unit
Add the calling thread to the IPC thread pool. This function does not return until the current process is exiting.
linkToDeath
open fun linkToDeath(
recipient: IBinder.DeathRecipient,
flags: Int
): Unit
Local implementation is a no-op.
Parameters | |
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recipient |
IBinder.DeathRecipient: This value cannot be null . |
Exceptions | |
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android.os.RemoteException |
if the target IBinder's process has already died. |
pingBinder
open fun pingBinder(): Boolean
Default implementation always returns true -- if you got here, the object is alive.
Return | |
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Boolean |
Returns false if the hosting process is gone, otherwise the result (always by default true) returned by the pingBinder() implementation on the other side. |
queryLocalInterface
open fun queryLocalInterface(descriptor: String): IInterface?
Use information supplied to attachInterface()
to return the associated IInterface
if it matches the requested descriptor.
Parameters | |
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descriptor |
String: This value cannot be null . |
Return | |
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IInterface? |
This value may be null . |
restoreCallingIdentity
static fun restoreCallingIdentity(token: Long): Unit
Restore the identity of the incoming IPC on the current thread back to a previously identity that was returned by clearCallingIdentity
.
Parameters | |
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token |
Long: The opaque token that was previously returned by clearCallingIdentity . |
See Also
restoreCallingWorkSource
static fun restoreCallingWorkSource(token: Long): Unit
Restores the work source on this thread using a token returned by setCallingWorkSourceUid(int)
or clearCallingWorkSource()
.
A typical use case would be
long token = Binder.setCallingWorkSourceUid(uid); try { // Call an API. } finally { Binder.restoreCallingWorkSource(token); }
setCallingWorkSourceUid
static fun setCallingWorkSourceUid(workSource: Int): Long
Sets the work source for this thread.
All the following binder calls on this thread will use the provided work source. If this is called during an on-going binder transaction, all the following binder calls will use the work source until the end of the transaction.
The concept of worksource is similar to WorkSource
. However, for performance reasons, we only support one UID. This UID represents the original user responsible for the binder calls.
restoreCallingWorkSource(long)
must always be called after setting the worksource.
A typical use case would be
long token = Binder.setCallingWorkSourceUid(uid); try { // Call an API. } finally { Binder.restoreCallingWorkSource(token); }
The work source will be propagated for future outgoing binder transactions executed on this thread.
Parameters | |
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workSource |
Int: The original UID responsible for the binder call. |
Return | |
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Long |
token to restore original work source. |
transact
fun transact(
code: Int,
data: Parcel,
reply: Parcel?,
flags: Int
): Boolean
Default implementation rewinds the parcels and calls onTransact. On the remote side, transact calls into the binder to do the IPC.
Parameters | |
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code |
Int: The action to perform. This should be a number between FIRST_CALL_TRANSACTION and LAST_CALL_TRANSACTION . |
data |
Parcel: This value cannot be null . |
reply |
Parcel?: This value may be null . |
flags |
Int: Additional operation flags. Either 0 for a normal RPC, or FLAG_ONEWAY for a one-way RPC. |
Return | |
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Boolean |
Returns the result from Binder#onTransact . A successful call generally returns true; false generally means the transaction code was not understood. For a oneway call to a different process false should never be returned. If a oneway call is made to code in the same process (usually to a C++ or Rust implementation), then there are no oneway semantics, and false can still be returned. |
unlinkToDeath
open fun unlinkToDeath(
recipient: IBinder.DeathRecipient,
flags: Int
): Boolean
Local implementation is a no-op.
Parameters | |
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recipient |
IBinder.DeathRecipient: This value cannot be null . |
Return | |
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Boolean |
true if the recipient is successfully unlinked, assuring you that its android.os.IBinder.DeathRecipient#binderDied method will not be called; false if the target IBinder has already died, meaning the method has been (or soon will be) called. |
Exceptions | |
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java.util.NoSuchElementException |
if the given recipient has not been registered with the IBinder, and the IBinder is still alive. Note that if the recipient was never registered, but the IBinder has already died, then this exception will not be thrown, and you will receive a false return value instead. |
Protected methods
dump
protected open fun dump(
fd: FileDescriptor,
fout: PrintWriter,
args: Array<String!>?
): Unit
Print the object's state into the given stream.
Parameters | |
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fd |
FileDescriptor: The raw file descriptor that the dump is being sent to. This value cannot be null . |
fout |
PrintWriter: The file to which you should dump your state. This will be closed for you after you return. This value cannot be null . |
args |
Array<String!>?: additional arguments to the dump request. This value may be null . |
onTransact
protected open fun onTransact(
code: Int,
data: Parcel,
reply: Parcel?,
flags: Int
): Boolean
Default implementation is a stub that returns false. You will want to override this to do the appropriate unmarshalling of transactions.
If you want to call this, call transact().
Implementations that are returning a result should generally use Parcel.writeNoException
and Parcel.writeException
to propagate exceptions back to the caller.
Parameters | |
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code |
Int: The action to perform. This should be a number between FIRST_CALL_TRANSACTION and LAST_CALL_TRANSACTION . |
data |
Parcel: Marshalled data being received from the caller. This value cannot be null . |
reply |
Parcel?: If the caller is expecting a result back, it should be marshalled in to here. This value may be null . |
flags |
Int: Additional operation flags. Either 0 for a normal RPC, or FLAG_ONEWAY for a one-way RPC. |
Return | |
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Boolean |
Return true on a successful call; returning false is generally used to indicate that you did not understand the transaction code. |