Looper

Summary

Enumerations
`Anonymous Enum 48{ ALOOPER_PREPARE_ALLOW_NON_CALLBACKS = 1<<0 }`	enum Option for for ALooper_prepare().
`Anonymous Enum 49{ ALOOPER_POLL_WAKE = -1, ALOOPER_POLL_CALLBACK = -2, ALOOPER_POLL_TIMEOUT = -3, ALOOPER_POLL_ERROR = -4 }`	enum Result from ALooper_pollOnce() and ALooper_pollAll().
`Anonymous Enum 50{ ALOOPER_EVENT_INPUT = 1 << 0, ALOOPER_EVENT_OUTPUT = 1 << 1, ALOOPER_EVENT_ERROR = 1 << 2, ALOOPER_EVENT_HANGUP = 1 << 3, ALOOPER_EVENT_INVALID = 1 << 4 }`	enum Flags for file descriptor events that a looper can monitor.

Typedefs
`ALooper`	typedef `struct ALooper` ALooper.
`ALooper_callbackFunc)(int fd, int events, void *data)`	typedef `int(*` For callback-based event loops, this is the prototype of the function that is called when a file descriptor event occurs.

Variables
`information`	`int ALooper_pollAll may ignore wakes Use ALooper_pollOnce instead See The API documentation for more`

Functions
`ALooper_acquire(ALooper *looper)`	`void` Acquire a reference on the given ALooper object.
`ALooper_addFd(ALooper looper, int fd, int ident, int events, ALooper_callbackFunc callback, void data)`	`int` Adds a new file descriptor to be polled by the looper.
`ALooper_forThread()`	`ALooper *` Returns the looper associated with the calling thread, or NULL if there is not one.
`ALooper_pollAll(int timeoutMillis, int outFd, int outEvents, void **outData) __REMOVED_IN(1`	`int` Deprecated. Calls to ALooper_pollAll should be replaced with ALooper_pollOnce. If you call ALooper_pollOnce in a loop, you must treat all return values as if they also indicate ALOOPER_POLL_WAKE. Like ALooper_pollOnce(), but performs all pending callbacks until all data has been consumed or a file descriptor is available with no callback.
`ALooper_pollOnce(int timeoutMillis, int outFd, int outEvents, void **outData)`	`int` Waits for events to be available, with optional timeout in milliseconds.
`ALooper_prepare(int opts)`	`ALooper *` Prepares a looper associated with the calling thread, and returns it.
`ALooper_release(ALooper *looper)`	`void` Remove a reference that was previously acquired with ALooper_acquire().
`ALooper_removeFd(ALooper *looper, int fd)`	`int` Removes a previously added file descriptor from the looper.
`ALooper_wake(ALooper *looper)`	`void` Wakes the poll asynchronously.

Enumerations

Anonymous Enum 48

Declared in android/looper.h

 Anonymous Enum 48

Option for for ALooper_prepare().

Properties

Properties
`ALOOPER_PREPARE_ALLOW_NON_CALLBACKS`	This looper will accept calls to ALooper_addFd() that do not have a callback (that is provide NULL for the callback). In this case the caller of ALooper_pollOnce() or ALooper_pollAll() MUST check the return from these functions to discover when data is available on such fds and process it.

ALOOPER_PREPARE_ALLOW_NON_CALLBACKS

This looper will accept calls to ALooper_addFd() that do not have a callback (that is provide NULL for the callback).

In this case the caller of ALooper_pollOnce() or ALooper_pollAll() MUST check the return from these functions to discover when data is available on such fds and process it.

Anonymous Enum 49

Declared in android/looper.h

 Anonymous Enum 49

Result from ALooper_pollOnce() and ALooper_pollAll().

Properties
`ALOOPER_POLL_CALLBACK`	Result from ALooper_pollOnce() and ALooper_pollAll(): One or more callbacks were executed.
`ALOOPER_POLL_ERROR`	Result from ALooper_pollOnce() and ALooper_pollAll(): An error occurred.
`ALOOPER_POLL_TIMEOUT`	Result from ALooper_pollOnce() and ALooper_pollAll(): The timeout expired.
`ALOOPER_POLL_WAKE`	The poll was awoken using wake() before the timeout expired and no callbacks were executed and no other file descriptors were ready.

Anonymous Enum 50

Declared in android/looper.h

 Anonymous Enum 50

Flags for file descriptor events that a looper can monitor.

These flag bits can be combined to monitor multiple events at once.

Properties
`ALOOPER_EVENT_ERROR`	The file descriptor has encountered an error condition. The looper always sends notifications about errors; it is not necessary to specify this event flag in the requested event set.
`ALOOPER_EVENT_HANGUP`	The file descriptor was hung up. For example, indicates that the remote end of a pipe or socket was closed. The looper always sends notifications about hangups; it is not necessary to specify this event flag in the requested event set.
`ALOOPER_EVENT_INPUT`	The file descriptor is available for read operations.
`ALOOPER_EVENT_INVALID`	The file descriptor is invalid. For example, the file descriptor was closed prematurely. The looper always sends notifications about invalid file descriptors; it is not necessary to specify this event flag in the requested event set.
`ALOOPER_EVENT_OUTPUT`	The file descriptor is available for write operations.

Typedefs

ALooper

Declared in android/looper.h

struct ALooper ALooper

ALooper.

A looper is the state tracking an event loop for a thread. Loopers do not define event structures or other such things; rather they are a lower-level facility to attach one or more discrete objects listening for an event. An "event" here is simply data available on a file descriptor: each attached object has an associated file descriptor, and waiting for "events" means (internally) polling on all of these file descriptors until one or more of them have data available.

A thread can have only one ALooper associated with it.

ALooper_callbackFunc

Declared in android/looper.h

int(* ALooper_callbackFunc)(int fd, int events, void *data)

For callback-based event loops, this is the prototype of the function that is called when a file descriptor event occurs.

It is given the file descriptor it is associated with, a bitmask of the poll events that were triggered (typically ALOOPER_EVENT_INPUT), and the data pointer that was originally supplied.

Implementations should return 1 to continue receiving callbacks, or 0 to have this file descriptor and callback unregistered from the looper.

Variables

information

Declared in android/looper.h

int ALooper_pollAll may ignore wakes Use ALooper_pollOnce instead See The API documentation for more information

Functions

ALooper_acquire

Declared in android/looper.h

void ALooper_acquire(
  ALooper *looper
)

Acquire a reference on the given ALooper object.

This prevents the object from being deleted until the reference is removed. This is only needed to safely hand an ALooper from one thread to another.

ALooper_addFd

Declared in android/looper.h

int ALooper_addFd(
  ALooper *looper,
  int fd,
  int ident,
  int events,
  ALooper_callbackFunc callback,
  void *data
)

Adds a new file descriptor to be polled by the looper.

If the same file descriptor was previously added, it is replaced.

"fd" is the file descriptor to be added. "ident" is an identifier for this event, which is returned from ALooper_pollOnce(). The identifier must be >= 0, or ALOOPER_POLL_CALLBACK if providing a non-NULL callback. "events" are the poll events to wake up on. Typically this is ALOOPER_EVENT_INPUT. "callback" is the function to call when there is an event on the file descriptor. "data" is a private data pointer to supply to the callback.

There are two main uses of this function:

(1) If "callback" is non-NULL, then this function will be called when there is data on the file descriptor. It should execute any events it has pending, appropriately reading from the file descriptor. The 'ident' is ignored in this case.

(2) If "callback" is NULL, the 'ident' will be returned by ALooper_pollOnce when its file descriptor has data available, requiring the caller to take care of processing it.

Returns 1 if the file descriptor was added or -1 if an error occurred.

This method can be called on any thread. This method may block briefly if it needs to wake the poll.

ALooper_forThread

Declared in android/looper.h

ALooper * ALooper_forThread()

Returns the looper associated with the calling thread, or NULL if there is not one.

ALooper_pollAll

Declared in android/looper.h

int ALooper_pollAll(
  int timeoutMillis,
  int *outFd,
  int *outEvents,
  void **outData
) __REMOVED_IN(1

Like ALooper_pollOnce(), but performs all pending callbacks until all data has been consumed or a file descriptor is available with no callback.

This function will never return ALOOPER_POLL_CALLBACK.

This API cannot be used safely, but a safe alternative exists (see below). As such, new builds will not be able to call this API and must migrate to the safe API. Binary compatibility is preserved to support already-compiled apps.

Deprecated. Calls to ALooper_pollAll should be replaced with ALooper_pollOnce. If you call ALooper_pollOnce in a loop, you must treat all return values as if they also indicate ALOOPER_POLL_WAKE.

ALooper_pollOnce

Declared in android/looper.h

int ALooper_pollOnce(
  int timeoutMillis,
  int *outFd,
  int *outEvents,
  void **outData
)

Waits for events to be available, with optional timeout in milliseconds.

Invokes callbacks for all file descriptors on which an event occurred.

If the timeout is zero, returns immediately without blocking. If the timeout is negative, waits indefinitely until an event appears.

Returns ALOOPER_POLL_WAKE if the poll was awoken using ALooper_wake() before the timeout expired and no callbacks were invoked and no other file descriptors were ready. All return values may also imply ALOOPER_POLL_WAKE.

Returns ALOOPER_POLL_CALLBACK if one or more callbacks were invoked. The poll may also have been explicitly woken by ALooper_wake.

Returns ALOOPER_POLL_TIMEOUT if there was no data before the given timeout expired. The poll may also have been explicitly woken by ALooper_wake.

Returns ALOOPER_POLL_ERROR if the calling thread has no associated Looper or for unrecoverable internal errors. The poll may also have been explicitly woken by ALooper_wake.

Returns a value >= 0 containing an identifier (the same identifier ident passed to ALooper_addFd()) if its file descriptor has data and it has no callback function (requiring the caller here to handle it). In this (and only this) case outFd, outEvents and outData will contain the poll events and data associated with the fd, otherwise they will be set to NULL. The poll may also have been explicitly woken by ALooper_wake.

This method does not return until it has finished invoking the appropriate callbacks for all file descriptors that were signalled.

ALooper_prepare

Declared in android/looper.h

ALooper * ALooper_prepare(
  int opts
)

Prepares a looper associated with the calling thread, and returns it.

If the thread already has a looper, it is returned. Otherwise, a new one is created, associated with the thread, and returned.

The opts may be ALOOPER_PREPARE_ALLOW_NON_CALLBACKS or 0.

ALooper_release

Declared in android/looper.h

void ALooper_release(
  ALooper *looper
)

Remove a reference that was previously acquired with ALooper_acquire().

ALooper_removeFd

Declared in android/looper.h

int ALooper_removeFd(
  ALooper *looper,
  int fd
)

Removes a previously added file descriptor from the looper.

When this method returns, it is safe to close the file descriptor since the looper will no longer have a reference to it. However, it is possible for the callback to already be running or for it to run one last time if the file descriptor was already signalled. Calling code is responsible for ensuring that this case is safely handled. For example, if the callback takes care of removing itself during its own execution either by returning 0 or by calling this method, then it can be guaranteed to not be invoked again at any later time unless registered anew.

Returns 1 if the file descriptor was removed, 0 if none was previously registered or -1 if an error occurred.

This method can be called on any thread. This method may block briefly if it needs to wake the poll.

ALooper_wake

Declared in android/looper.h

void ALooper_wake(
  ALooper *looper
)

Wakes the poll asynchronously.

This method can be called on any thread. This method returns immediately.