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Looper

Files

file  looper.h
 

Typedefs

typedef struct ALooper ALooper
 
typedef int(* ALooper_callbackFunc) (int fd, int events, void *data)
 

Enumerations

enum  { ALOOPER_PREPARE_ALLOW_NON_CALLBACKS = 1<<0 }
 
enum  { ALOOPER_POLL_WAKE = -1, ALOOPER_POLL_CALLBACK = -2, ALOOPER_POLL_TIMEOUT = -3, ALOOPER_POLL_ERROR = -4 }
 
enum  {
  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
}
 

Functions

ALooperALooper_forThread ()
 
ALooperALooper_prepare (int opts)
 
void ALooper_acquire (ALooper *looper)
 
void ALooper_release (ALooper *looper)
 
int ALooper_pollOnce (int timeoutMillis, int *outFd, int *outEvents, void **outData)
 
int ALooper_pollAll (int timeoutMillis, int *outFd, int *outEvents, void **outData)
 
void ALooper_wake (ALooper *looper)
 
int ALooper_addFd (ALooper *looper, int fd, int ident, int events, ALooper_callbackFunc callback, void *data)
 
int ALooper_removeFd (ALooper *looper, int fd)
 

Detailed Description

Typedef Documentation

§ ALooper

typedef 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

typedef 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.

Enumeration Type Documentation

§ anonymous enum

anonymous enum

Option for for ALooper_prepare().

Enumerator
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

anonymous enum

Result from ALooper_pollOnce() and ALooper_pollAll().

Enumerator
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.

ALOOPER_POLL_CALLBACK 

Result from ALooper_pollOnce() and ALooper_pollAll(): One or more callbacks were executed.

ALOOPER_POLL_TIMEOUT 

Result from ALooper_pollOnce() and ALooper_pollAll(): The timeout expired.

ALOOPER_POLL_ERROR 

Result from ALooper_pollOnce() and ALooper_pollAll(): An error occurred.

§ anonymous enum

anonymous enum

Flags for file descriptor events that a looper can monitor.

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

Enumerator
ALOOPER_EVENT_INPUT 

The file descriptor is available for read operations.

ALOOPER_EVENT_OUTPUT 

The file descriptor is available for write operations.

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_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.

Function Documentation

§ ALooper_acquire()

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()

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()

ALooper* ALooper_forThread ( )

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

§ ALooper_pollAll()

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

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.

§ ALooper_pollOnce()

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 wake() before the timeout expired and no callbacks were invoked and no other file descriptors were ready.

Returns ALOOPER_POLL_CALLBACK if one or more callbacks were invoked.

Returns ALOOPER_POLL_TIMEOUT if there was no data before the given timeout expired.

Returns ALOOPER_POLL_ERROR if an error occurred.

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.

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

§ ALooper_prepare()

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()

void ALooper_release ( ALooper looper)

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

§ ALooper_removeFd()

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()

void ALooper_wake ( ALooper looper)

Wakes the poll asynchronously.

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

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