1 /*
2  * Copyright (C) 2010 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 
18 #ifndef ANDROID_LOOPER_H
19 #define ANDROID_LOOPER_H
20 
21 #ifdef __cplusplus
22 extern "C" {
23 #endif
24 
25 /**
26  * ALooper
27  *
28  * A looper is the state tracking an event loop for a thread.
29  * Loopers do not define event structures or other such things; rather
30  * they are a lower-level facility to attach one or more discrete objects
31  * listening for an event.  An "event" here is simply data available on
32  * a file descriptor: each attached object has an associated file descriptor,
33  * and waiting for "events" means (internally) polling on all of these file
34  * descriptors until one or more of them have data available.
35  *
36  * A thread can have only one ALooper associated with it.
37  */
38 struct ALooper;
39 typedef struct ALooper ALooper;
40 
41 /**
42  * Returns the looper associated with the calling thread, or NULL if
43  * there is not one.
44  */
45 ALooper* ALooper_forThread();
46 
47 enum {
48     /**
49      * Option for ALooper_prepare: this looper will accept calls to
50      * ALooper_addFd() that do not have a callback (that is provide NULL
51      * for the callback).  In this case the caller of ALooper_pollOnce()
52      * or ALooper_pollAll() MUST check the return from these functions to
53      * discover when data is available on such fds and process it.
54      */
55     ALOOPER_PREPARE_ALLOW_NON_CALLBACKS = 1<<0
56 };
57 
58 /**
59  * Prepares a looper associated with the calling thread, and returns it.
60  * If the thread already has a looper, it is returned.  Otherwise, a new
61  * one is created, associated with the thread, and returned.
62  *
63  * The opts may be ALOOPER_PREPARE_ALLOW_NON_CALLBACKS or 0.
64  */
65 ALooper* ALooper_prepare(int opts);
66 
67 enum {
68     /**
69      * Result from ALooper_pollOnce() and ALooper_pollAll():
70      * The poll was awoken using wake() before the timeout expired
71      * and no callbacks were executed and no other file descriptors were ready.
72      */
73     ALOOPER_POLL_WAKE = -1,
74 
75     /**
76      * Result from ALooper_pollOnce() and ALooper_pollAll():
77      * One or more callbacks were executed.
78      */
79     ALOOPER_POLL_CALLBACK = -2,
80 
81     /**
82      * Result from ALooper_pollOnce() and ALooper_pollAll():
83      * The timeout expired.
84      */
85     ALOOPER_POLL_TIMEOUT = -3,
86 
87     /**
88      * Result from ALooper_pollOnce() and ALooper_pollAll():
89      * An error occurred.
90      */
91     ALOOPER_POLL_ERROR = -4,
92 };
93 
94 /**
95  * Acquire a reference on the given ALooper object.  This prevents the object
96  * from being deleted until the reference is removed.  This is only needed
97  * to safely hand an ALooper from one thread to another.
98  */
99 void ALooper_acquire(ALooper* looper);
100 
101 /**
102  * Remove a reference that was previously acquired with ALooper_acquire().
103  */
104 void ALooper_release(ALooper* looper);
105 
106 /**
107  * Flags for file descriptor events that a looper can monitor.
108  *
109  * These flag bits can be combined to monitor multiple events at once.
110  */
111 enum {
112     /**
113      * The file descriptor is available for read operations.
114      */
115     ALOOPER_EVENT_INPUT = 1 << 0,
116 
117     /**
118      * The file descriptor is available for write operations.
119      */
120     ALOOPER_EVENT_OUTPUT = 1 << 1,
121 
122     /**
123      * The file descriptor has encountered an error condition.
124      *
125      * The looper always sends notifications about errors; it is not necessary
126      * to specify this event flag in the requested event set.
127      */
128     ALOOPER_EVENT_ERROR = 1 << 2,
129 
130     /**
131      * The file descriptor was hung up.
132      * For example, indicates that the remote end of a pipe or socket was closed.
133      *
134      * The looper always sends notifications about hangups; it is not necessary
135      * to specify this event flag in the requested event set.
136      */
137     ALOOPER_EVENT_HANGUP = 1 << 3,
138 
139     /**
140      * The file descriptor is invalid.
141      * For example, the file descriptor was closed prematurely.
142      *
143      * The looper always sends notifications about invalid file descriptors; it is not necessary
144      * to specify this event flag in the requested event set.
145      */
146     ALOOPER_EVENT_INVALID = 1 << 4,
147 };
148 
149 /**
150  * For callback-based event loops, this is the prototype of the function
151  * that is called when a file descriptor event occurs.
152  * It is given the file descriptor it is associated with,
153  * a bitmask of the poll events that were triggered (typically ALOOPER_EVENT_INPUT),
154  * and the data pointer that was originally supplied.
155  *
156  * Implementations should return 1 to continue receiving callbacks, or 0
157  * to have this file descriptor and callback unregistered from the looper.
158  */
159 typedef int (*ALooper_callbackFunc)(int fd, int events, void* data);
160 
161 /**
162  * Waits for events to be available, with optional timeout in milliseconds.
163  * Invokes callbacks for all file descriptors on which an event occurred.
164  *
165  * If the timeout is zero, returns immediately without blocking.
166  * If the timeout is negative, waits indefinitely until an event appears.
167  *
168  * Returns ALOOPER_POLL_WAKE if the poll was awoken using wake() before
169  * the timeout expired and no callbacks were invoked and no other file
170  * descriptors were ready.
171  *
172  * Returns ALOOPER_POLL_CALLBACK if one or more callbacks were invoked.
173  *
174  * Returns ALOOPER_POLL_TIMEOUT if there was no data before the given
175  * timeout expired.
176  *
177  * Returns ALOOPER_POLL_ERROR if an error occurred.
178  *
179  * Returns a value >= 0 containing an identifier if its file descriptor has data
180  * and it has no callback function (requiring the caller here to handle it).
181  * In this (and only this) case outFd, outEvents and outData will contain the poll
182  * events and data associated with the fd, otherwise they will be set to NULL.
183  *
184  * This method does not return until it has finished invoking the appropriate callbacks
185  * for all file descriptors that were signalled.
186  */
187 int ALooper_pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData);
188 
189 /**
190  * Like ALooper_pollOnce(), but performs all pending callbacks until all
191  * data has been consumed or a file descriptor is available with no callback.
192  * This function will never return ALOOPER_POLL_CALLBACK.
193  */
194 int ALooper_pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData);
195 
196 /**
197  * Wakes the poll asynchronously.
198  *
199  * This method can be called on any thread.
200  * This method returns immediately.
201  */
202 void ALooper_wake(ALooper* looper);
203 
204 /**
205  * Adds a new file descriptor to be polled by the looper.
206  * If the same file descriptor was previously added, it is replaced.
207  *
208  * "fd" is the file descriptor to be added.
209  * "ident" is an identifier for this event, which is returned from ALooper_pollOnce().
210  * The identifier must be >= 0, or ALOOPER_POLL_CALLBACK if providing a non-NULL callback.
211  * "events" are the poll events to wake up on.  Typically this is ALOOPER_EVENT_INPUT.
212  * "callback" is the function to call when there is an event on the file descriptor.
213  * "data" is a private data pointer to supply to the callback.
214  *
215  * There are two main uses of this function:
216  *
217  * (1) If "callback" is non-NULL, then this function will be called when there is
218  * data on the file descriptor.  It should execute any events it has pending,
219  * appropriately reading from the file descriptor.  The 'ident' is ignored in this case.
220  *
221  * (2) If "callback" is NULL, the 'ident' will be returned by ALooper_pollOnce
222  * when its file descriptor has data available, requiring the caller to take
223  * care of processing it.
224  *
225  * Returns 1 if the file descriptor was added or -1 if an error occurred.
226  *
227  * This method can be called on any thread.
228  * This method may block briefly if it needs to wake the poll.
229  */
230 int ALooper_addFd(ALooper* looper, int fd, int ident, int events,
231         ALooper_callbackFunc callback, void* data);
232 
233 /**
234  * Removes a previously added file descriptor from the looper.
235  *
236  * When this method returns, it is safe to close the file descriptor since the looper
237  * will no longer have a reference to it.  However, it is possible for the callback to
238  * already be running or for it to run one last time if the file descriptor was already
239  * signalled.  Calling code is responsible for ensuring that this case is safely handled.
240  * For example, if the callback takes care of removing itself during its own execution either
241  * by returning 0 or by calling this method, then it can be guaranteed to not be invoked
242  * again at any later time unless registered anew.
243  *
244  * Returns 1 if the file descriptor was removed, 0 if none was previously registered
245  * or -1 if an error occurred.
246  *
247  * This method can be called on any thread.
248  * This method may block briefly if it needs to wake the poll.
249  */
250 int ALooper_removeFd(ALooper* looper, int fd);
251 
252 #ifdef __cplusplus
253 };
254 #endif
255 
256 #endif // ANDROID_LOOPER_H
257