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 * @addtogroup Looper 19 * @{ 20 */ 21 22 /** 23 * @file looper.h 24 */ 25 26 #ifndef ANDROID_LOOPER_H 27 #define ANDROID_LOOPER_H 28 29 #ifdef __cplusplus 30 extern "C" { 31 #endif 32 33 struct ALooper; 34 /** 35 * ALooper 36 * 37 * A looper is the state tracking an event loop for a thread. 38 * Loopers do not define event structures or other such things; rather 39 * they are a lower-level facility to attach one or more discrete objects 40 * listening for an event. An "event" here is simply data available on 41 * a file descriptor: each attached object has an associated file descriptor, 42 * and waiting for "events" means (internally) polling on all of these file 43 * descriptors until one or more of them have data available. 44 * 45 * A thread can have only one ALooper associated with it. 46 */ 47 typedef struct ALooper ALooper; 48 49 /** 50 * Returns the looper associated with the calling thread, or NULL if 51 * there is not one. 52 */ 53 ALooper* ALooper_forThread(); 54 55 /** Option for for ALooper_prepare(). */ 56 enum { 57 /** 58 * This looper will accept calls to ALooper_addFd() that do not 59 * have a callback (that is provide NULL for the callback). In 60 * this case the caller of ALooper_pollOnce() or ALooper_pollAll() 61 * MUST check the return from these functions to discover when 62 * data is available on such fds and process it. 63 */ 64 ALOOPER_PREPARE_ALLOW_NON_CALLBACKS = 1<<0 65 }; 66 67 /** 68 * Prepares a looper associated with the calling thread, and returns it. 69 * If the thread already has a looper, it is returned. Otherwise, a new 70 * one is created, associated with the thread, and returned. 71 * 72 * The opts may be ALOOPER_PREPARE_ALLOW_NON_CALLBACKS or 0. 73 */ 74 ALooper* ALooper_prepare(int opts); 75 76 /** Result from ALooper_pollOnce() and ALooper_pollAll(). */ 77 enum { 78 /** 79 * The poll was awoken using wake() before the timeout expired 80 * and no callbacks were executed and no other file descriptors were ready. 81 */ 82 ALOOPER_POLL_WAKE = -1, 83 84 /** 85 * Result from ALooper_pollOnce() and ALooper_pollAll(): 86 * One or more callbacks were executed. 87 */ 88 ALOOPER_POLL_CALLBACK = -2, 89 90 /** 91 * Result from ALooper_pollOnce() and ALooper_pollAll(): 92 * The timeout expired. 93 */ 94 ALOOPER_POLL_TIMEOUT = -3, 95 96 /** 97 * Result from ALooper_pollOnce() and ALooper_pollAll(): 98 * An error occurred. 99 */ 100 ALOOPER_POLL_ERROR = -4, 101 }; 102 103 /** 104 * Acquire a reference on the given ALooper object. This prevents the object 105 * from being deleted until the reference is removed. This is only needed 106 * to safely hand an ALooper from one thread to another. 107 */ 108 void ALooper_acquire(ALooper* looper); 109 110 /** 111 * Remove a reference that was previously acquired with ALooper_acquire(). 112 */ 113 void ALooper_release(ALooper* looper); 114 115 /** 116 * Flags for file descriptor events that a looper can monitor. 117 * 118 * These flag bits can be combined to monitor multiple events at once. 119 */ 120 enum { 121 /** 122 * The file descriptor is available for read operations. 123 */ 124 ALOOPER_EVENT_INPUT = 1 << 0, 125 126 /** 127 * The file descriptor is available for write operations. 128 */ 129 ALOOPER_EVENT_OUTPUT = 1 << 1, 130 131 /** 132 * The file descriptor has encountered an error condition. 133 * 134 * The looper always sends notifications about errors; it is not necessary 135 * to specify this event flag in the requested event set. 136 */ 137 ALOOPER_EVENT_ERROR = 1 << 2, 138 139 /** 140 * The file descriptor was hung up. 141 * For example, indicates that the remote end of a pipe or socket was closed. 142 * 143 * The looper always sends notifications about hangups; it is not necessary 144 * to specify this event flag in the requested event set. 145 */ 146 ALOOPER_EVENT_HANGUP = 1 << 3, 147 148 /** 149 * The file descriptor is invalid. 150 * For example, the file descriptor was closed prematurely. 151 * 152 * The looper always sends notifications about invalid file descriptors; it is not necessary 153 * to specify this event flag in the requested event set. 154 */ 155 ALOOPER_EVENT_INVALID = 1 << 4, 156 }; 157 158 /** 159 * For callback-based event loops, this is the prototype of the function 160 * that is called when a file descriptor event occurs. 161 * It is given the file descriptor it is associated with, 162 * a bitmask of the poll events that were triggered (typically ALOOPER_EVENT_INPUT), 163 * and the data pointer that was originally supplied. 164 * 165 * Implementations should return 1 to continue receiving callbacks, or 0 166 * to have this file descriptor and callback unregistered from the looper. 167 */ 168 typedef int (*ALooper_callbackFunc)(int fd, int events, void* data); 169 170 /** 171 * Waits for events to be available, with optional timeout in milliseconds. 172 * Invokes callbacks for all file descriptors on which an event occurred. 173 * 174 * If the timeout is zero, returns immediately without blocking. 175 * If the timeout is negative, waits indefinitely until an event appears. 176 * 177 * Returns ALOOPER_POLL_WAKE if the poll was awoken using wake() before 178 * the timeout expired and no callbacks were invoked and no other file 179 * descriptors were ready. 180 * 181 * Returns ALOOPER_POLL_CALLBACK if one or more callbacks were invoked. 182 * 183 * Returns ALOOPER_POLL_TIMEOUT if there was no data before the given 184 * timeout expired. 185 * 186 * Returns ALOOPER_POLL_ERROR if an error occurred. 187 * 188 * Returns a value >= 0 containing an identifier (the same identifier 189 * `ident` passed to ALooper_addFd()) if its file descriptor has data 190 * and it has no callback function (requiring the caller here to 191 * handle it). In this (and only this) case outFd, outEvents and 192 * outData will contain the poll events and data associated with the 193 * fd, otherwise they will be set to NULL. 194 * 195 * This method does not return until it has finished invoking the appropriate callbacks 196 * for all file descriptors that were signalled. 197 */ 198 int ALooper_pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData); 199 200 /** 201 * Like ALooper_pollOnce(), but performs all pending callbacks until all 202 * data has been consumed or a file descriptor is available with no callback. 203 * This function will never return ALOOPER_POLL_CALLBACK. 204 */ 205 int ALooper_pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData); 206 207 /** 208 * Wakes the poll asynchronously. 209 * 210 * This method can be called on any thread. 211 * This method returns immediately. 212 */ 213 void ALooper_wake(ALooper* looper); 214 215 /** 216 * Adds a new file descriptor to be polled by the looper. 217 * If the same file descriptor was previously added, it is replaced. 218 * 219 * "fd" is the file descriptor to be added. 220 * "ident" is an identifier for this event, which is returned from ALooper_pollOnce(). 221 * The identifier must be >= 0, or ALOOPER_POLL_CALLBACK if providing a non-NULL callback. 222 * "events" are the poll events to wake up on. Typically this is ALOOPER_EVENT_INPUT. 223 * "callback" is the function to call when there is an event on the file descriptor. 224 * "data" is a private data pointer to supply to the callback. 225 * 226 * There are two main uses of this function: 227 * 228 * (1) If "callback" is non-NULL, then this function will be called when there is 229 * data on the file descriptor. It should execute any events it has pending, 230 * appropriately reading from the file descriptor. The 'ident' is ignored in this case. 231 * 232 * (2) If "callback" is NULL, the 'ident' will be returned by ALooper_pollOnce 233 * when its file descriptor has data available, requiring the caller to take 234 * care of processing it. 235 * 236 * Returns 1 if the file descriptor was added or -1 if an error occurred. 237 * 238 * This method can be called on any thread. 239 * This method may block briefly if it needs to wake the poll. 240 */ 241 int ALooper_addFd(ALooper* looper, int fd, int ident, int events, 242 ALooper_callbackFunc callback, void* data); 243 244 /** 245 * Removes a previously added file descriptor from the looper. 246 * 247 * When this method returns, it is safe to close the file descriptor since the looper 248 * will no longer have a reference to it. However, it is possible for the callback to 249 * already be running or for it to run one last time if the file descriptor was already 250 * signalled. Calling code is responsible for ensuring that this case is safely handled. 251 * For example, if the callback takes care of removing itself during its own execution either 252 * by returning 0 or by calling this method, then it can be guaranteed to not be invoked 253 * again at any later time unless registered anew. 254 * 255 * Returns 1 if the file descriptor was removed, 0 if none was previously registered 256 * or -1 if an error occurred. 257 * 258 * This method can be called on any thread. 259 * This method may block briefly if it needs to wake the poll. 260 */ 261 int ALooper_removeFd(ALooper* looper, int fd); 262 263 #ifdef __cplusplus 264 }; 265 #endif 266 267 #endif // ANDROID_LOOPER_H 268 269 /** @} */ 270
