summaryrefslogtreecommitdiffstats
path: root/include/android/looper.h
blob: 718f703048dcbd5dae976729f1df73327b37dc11 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @addtogroup Looper
 * @{
 */

/**
 * @file looper.h
 */

#ifndef ANDROID_LOOPER_H
#define ANDROID_LOOPER_H

#ifdef __cplusplus
extern "C" {
#endif

struct 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.
 */
typedef struct ALooper ALooper;

/**
 * Returns the looper associated with the calling thread, or NULL if
 * there is not one.
 */
ALooper* ALooper_forThread();

/** Option for for ALooper_prepare(). */
enum {
    /**
     * 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 = 1<<0
};

/**
 * 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* ALooper_prepare(int opts);

/** Result from ALooper_pollOnce() and ALooper_pollAll(). */
enum {
    /**
     * The poll was awoken using wake() before the timeout expired
     * and no callbacks were executed and no other file descriptors were ready.
     */
    ALOOPER_POLL_WAKE = -1,

    /**
     * Result from ALooper_pollOnce() and ALooper_pollAll():
     * One or more callbacks were executed.
     */
    ALOOPER_POLL_CALLBACK = -2,

    /**
     * Result from ALooper_pollOnce() and ALooper_pollAll():
     * The timeout expired.
     */
    ALOOPER_POLL_TIMEOUT = -3,

    /**
     * Result from ALooper_pollOnce() and ALooper_pollAll():
     * An error occurred.
     */
    ALOOPER_POLL_ERROR = -4,
};

/**
 * 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.
 */
void ALooper_acquire(ALooper* looper);

/**
 * Remove a reference that was previously acquired with ALooper_acquire().
 */
void ALooper_release(ALooper* looper);

/**
 * Flags for file descriptor events that a looper can monitor.
 *
 * These flag bits can be combined to monitor multiple events at once.
 */
enum {
    /**
     * The file descriptor is available for read operations.
     */
    ALOOPER_EVENT_INPUT = 1 << 0,

    /**
     * The file descriptor is available for write operations.
     */
    ALOOPER_EVENT_OUTPUT = 1 << 1,

    /**
     * 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_ERROR = 1 << 2,

    /**
     * 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_HANGUP = 1 << 3,

    /**
     * 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_INVALID = 1 << 4,
};

/**
 * 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.
 */
typedef int (*ALooper_callbackFunc)(int fd, int events, void* data);

/**
 * 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.
 */
int ALooper_pollOnce(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.
 */
int ALooper_pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData);

/**
 * Wakes the poll asynchronously.
 *
 * This method can be called on any thread.
 * This method returns immediately.
 */
void ALooper_wake(ALooper* looper);

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

/**
 * 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.
 */
int ALooper_removeFd(ALooper* looper, int fd);

#ifdef __cplusplus
};
#endif

#endif // ANDROID_LOOPER_H

/** @} */