dispatch/block.h

   1 /*
   2  * Copyright (c) 2014 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_APACHE_LICENSE_HEADER_START@
   5  *
   6  * Licensed under the Apache License, Version 2.0 (the "License");
   7  * you may not use this file except in compliance with the License.
   8  * You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  *
  18  * @APPLE_APACHE_LICENSE_HEADER_END@
  19  */
  20
  21 #ifndef __DISPATCH_BLOCK__
  22 #define __DISPATCH_BLOCK__
  23
  24 #ifndef __DISPATCH_INDIRECT__
  25 #error "Please #include <dispatch/dispatch.h> instead of this file directly."
  26 #include <dispatch/base.h> // for HeaderDoc
  27 #endif
  28
  29 #ifdef __BLOCKS__
  30
  31 /*!
  32  * @group Dispatch block objects
  33  */
  34
  35 DISPATCH_ASSUME_NONNULL_BEGIN
  36
  37 __BEGIN_DECLS
  38
  39 /*!
  40  * @typedef dispatch_block_flags_t
  41  * Flags to pass to the dispatch_block_create* functions.
  42  *
  43  * @const DISPATCH_BLOCK_BARRIER
  44  * Flag indicating that a dispatch block object should act as a barrier block
  45  * when submitted to a DISPATCH_QUEUE_CONCURRENT queue.
  46  * See dispatch_barrier_async() for details.
  47  * This flag has no effect when the dispatch block object is invoked directly.
  48  *
  49  * @const DISPATCH_BLOCK_DETACHED
  50  * Flag indicating that a dispatch block object should execute disassociated
  51  * from current execution context attributes such as QOS class, os_activity_t
  52  * and properties of the current IPC request (if any). If invoked directly, the
  53  * block object will remove these attributes from the calling thread for the
  54  * duration of the block body (before applying attributes assigned to the block
  55  * object, if any). If submitted to a queue, the block object will be executed
  56  * with the attributes of the queue (or any attributes specifically assigned to
  57  * the block object).
  58  *
  59  * @const DISPATCH_BLOCK_ASSIGN_CURRENT
  60  * Flag indicating that a dispatch block object should be assigned the execution
  61  * context attributes that are current at the time the block object is created.
  62  * This applies to attributes such as QOS class, os_activity_t and properties of
  63  * the current IPC request (if any). If invoked directly, the block object will
  64  * apply these attributes to the calling thread for the duration of the block
  65  * body. If the block object is submitted to a queue, this flag replaces the
  66  * default behavior of associating the submitted block instance with the
  67  * execution context attributes that are current at the time of submission.
  68  * If a specific QOS class is assigned with DISPATCH_BLOCK_NO_QOS_CLASS or
  69  * dispatch_block_create_with_qos_class(), that QOS class takes precedence over
  70  * the QOS class assignment indicated by this flag.
  71  *
  72  * @const DISPATCH_BLOCK_NO_QOS_CLASS
  73  * Flag indicating that a dispatch block object should be not be assigned a QOS
  74  * class. If invoked directly, the block object will be executed with the QOS
  75  * class of the calling thread. If the block object is submitted to a queue,
  76  * this replaces the default behavior of associating the submitted block
  77  * instance with the QOS class current at the time of submission.
  78  * This flag is ignored if a specific QOS class is assigned with
  79  * dispatch_block_create_with_qos_class().
  80  *
  81  * @const DISPATCH_BLOCK_INHERIT_QOS_CLASS
  82  * Flag indicating that execution of a dispatch block object submitted to a
  83  * queue should prefer the QOS class assigned to the queue over the QOS class
  84  * assigned to the block (resp. associated with the block at the time of
  85  * submission). The latter will only be used if the queue in question does not
  86  * have an assigned QOS class, as long as doing so does not result in a QOS
  87  * class lower than the QOS class inherited from the queue's target queue.
  88  * This flag is the default when a dispatch block object is submitted to a queue
  89  * for asynchronous execution and has no effect when the dispatch block object
  90  * is invoked directly. It is ignored if DISPATCH_BLOCK_ENFORCE_QOS_CLASS is
  91  * also passed.
  92  *
  93  * @const DISPATCH_BLOCK_ENFORCE_QOS_CLASS
  94  * Flag indicating that execution of a dispatch block object submitted to a
  95  * queue should prefer the QOS class assigned to the block (resp. associated
  96  * with the block at the time of submission) over the QOS class assigned to the
  97  * queue, as long as doing so will not result in a lower QOS class.
  98  * This flag is the default when a dispatch block object is submitted to a queue
  99  * for synchronous execution or when the dispatch block object is invoked
 100  * directly.
 101  */
 102 DISPATCH_ENUM(dispatch_block_flags, unsigned long,
 103         DISPATCH_BLOCK_BARRIER
 104                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x1,
 105         DISPATCH_BLOCK_DETACHED
 106                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x2,
 107         DISPATCH_BLOCK_ASSIGN_CURRENT
 108                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x4,
 109         DISPATCH_BLOCK_NO_QOS_CLASS
 110                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x8,
 111         DISPATCH_BLOCK_INHERIT_QOS_CLASS
 112                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x10,
 113         DISPATCH_BLOCK_ENFORCE_QOS_CLASS
 114                         DISPATCH_ENUM_API_AVAILABLE(macos(10.10), ios(8.0)) = 0x20,
 115 );
 116
 117 /*!
 118  * @function dispatch_block_create
 119  *
 120  * @abstract
 121  * Create a new dispatch block object on the heap from an existing block and
 122  * the given flags.
 123  *
 124  * @discussion
 125  * The provided block is Block_copy'ed to the heap and retained by the newly
 126  * created dispatch block object.
 127  *
 128  * The returned dispatch block object is intended to be submitted to a dispatch
 129  * queue with dispatch_async() and related functions, but may also be invoked
 130  * directly. Both operations can be performed an arbitrary number of times but
 131  * only the first completed execution of a dispatch block object can be waited
 132  * on with dispatch_block_wait() or observed with dispatch_block_notify().
 133  *
 134  * If the returned dispatch block object is submitted to a dispatch queue, the
 135  * submitted block instance will be associated with the QOS class current at the
 136  * time of submission, unless one of the following flags assigned a specific QOS
 137  * class (or no QOS class) at the time of block creation:
 138  *  - DISPATCH_BLOCK_ASSIGN_CURRENT
 139  *  - DISPATCH_BLOCK_NO_QOS_CLASS
 140  *  - DISPATCH_BLOCK_DETACHED
 141  * The QOS class the block object will be executed with also depends on the QOS
 142  * class assigned to the queue and which of the following flags was specified or
 143  * defaulted to:
 144  *  - DISPATCH_BLOCK_INHERIT_QOS_CLASS (default for asynchronous execution)
 145  *  - DISPATCH_BLOCK_ENFORCE_QOS_CLASS (default for synchronous execution)
 146  * See description of dispatch_block_flags_t for details.
 147  *
 148  * If the returned dispatch block object is submitted directly to a serial queue
 149  * and is configured to execute with a specific QOS class, the system will make
 150  * a best effort to apply the necessary QOS overrides to ensure that blocks
 151  * submitted earlier to the serial queue are executed at that same QOS class or
 152  * higher.
 153  *
 154  * @param flags
 155  * Configuration flags for the block object.
 156  * Passing a value that is not a bitwise OR of flags from dispatch_block_flags_t
 157  * results in NULL being returned.
 158  *
 159  * @param block
 160  * The block to create the dispatch block object from.
 161  *
 162  * @result
 163  * The newly created dispatch block object, or NULL.
 164  * When not building with Objective-C ARC, must be released with a -[release]
 165  * message or the Block_release() function.
 166  */
 167 API_AVAILABLE(macos(10.10), ios(8.0))
 168 DISPATCH_EXPORT DISPATCH_NONNULL2 DISPATCH_RETURNS_RETAINED_BLOCK
 169 DISPATCH_WARN_RESULT DISPATCH_NOTHROW
 170 dispatch_block_t
 171 dispatch_block_create(dispatch_block_flags_t flags, dispatch_block_t block);
 172
 173 /*!
 174  * @function dispatch_block_create_with_qos_class
 175  *
 176  * @abstract
 177  * Create a new dispatch block object on the heap from an existing block and
 178  * the given flags, and assign it the specified QOS class and relative priority.
 179  *
 180  * @discussion
 181  * The provided block is Block_copy'ed to the heap and retained by the newly
 182  * created dispatch block object.
 183  *
 184  * The returned dispatch block object is intended to be submitted to a dispatch
 185  * queue with dispatch_async() and related functions, but may also be invoked
 186  * directly. Both operations can be performed an arbitrary number of times but
 187  * only the first completed execution of a dispatch block object can be waited
 188  * on with dispatch_block_wait() or observed with dispatch_block_notify().
 189  *
 190  * If invoked directly, the returned dispatch block object will be executed with
 191  * the assigned QOS class as long as that does not result in a lower QOS class
 192  * than what is current on the calling thread.
 193  *
 194  * If the returned dispatch block object is submitted to a dispatch queue, the
 195  * QOS class it will be executed with depends on the QOS class assigned to the
 196  * block, the QOS class assigned to the queue and which of the following flags
 197  * was specified or defaulted to:
 198  *  - DISPATCH_BLOCK_INHERIT_QOS_CLASS: default for asynchronous execution
 199  *  - DISPATCH_BLOCK_ENFORCE_QOS_CLASS: default for synchronous execution
 200  * See description of dispatch_block_flags_t for details.
 201  *
 202  * If the returned dispatch block object is submitted directly to a serial queue
 203  * and is configured to execute with a specific QOS class, the system will make
 204  * a best effort to apply the necessary QOS overrides to ensure that blocks
 205  * submitted earlier to the serial queue are executed at that same QOS class or
 206  * higher.
 207  *
 208  * @param flags
 209  * Configuration flags for the new block object.
 210  * Passing a value that is not a bitwise OR of flags from dispatch_block_flags_t
 211  * results in NULL being returned.
 212  *
 213  * @param qos_class
 214  * A QOS class value:
 215  *  - QOS_CLASS_USER_INTERACTIVE
 216  *  - QOS_CLASS_USER_INITIATED
 217  *  - QOS_CLASS_DEFAULT
 218  *  - QOS_CLASS_UTILITY
 219  *  - QOS_CLASS_BACKGROUND
 220  *  - QOS_CLASS_UNSPECIFIED
 221  * Passing QOS_CLASS_UNSPECIFIED is equivalent to specifying the
 222  * DISPATCH_BLOCK_NO_QOS_CLASS flag. Passing any other value results in NULL
 223  * being returned.
 224  *
 225  * @param relative_priority
 226  * A relative priority within the QOS class. This value is a negative
 227  * offset from the maximum supported scheduler priority for the given class.
 228  * Passing a value greater than zero or less than QOS_MIN_RELATIVE_PRIORITY
 229  * results in NULL being returned.
 230  *
 231  * @param block
 232  * The block to create the dispatch block object from.
 233  *
 234  * @result
 235  * The newly created dispatch block object, or NULL.
 236  * When not building with Objective-C ARC, must be released with a -[release]
 237  * message or the Block_release() function.
 238  */
 239 API_AVAILABLE(macos(10.10), ios(8.0))
 240 DISPATCH_EXPORT DISPATCH_NONNULL4 DISPATCH_RETURNS_RETAINED_BLOCK
 241 DISPATCH_WARN_RESULT DISPATCH_NOTHROW
 242 dispatch_block_t
 243 dispatch_block_create_with_qos_class(dispatch_block_flags_t flags,
 244                 dispatch_qos_class_t qos_class, int relative_priority,
 245                 dispatch_block_t block);
 246
 247 /*!
 248  * @function dispatch_block_perform
 249  *
 250  * @abstract
 251  * Create, synchronously execute and release a dispatch block object from the
 252  * specified block and flags.
 253  *
 254  * @discussion
 255  * Behaves identically to the sequence
 256  * <code>
 257  * dispatch_block_t b = dispatch_block_create(flags, block);
 258  * b();
 259  * Block_release(b);
 260  * </code>
 261  * but may be implemented more efficiently internally by not requiring a copy
 262  * to the heap of the specified block or the allocation of a new block object.
 263  *
 264  * @param flags
 265  * Configuration flags for the temporary block object.
 266  * The result of passing a value that is not a bitwise OR of flags from
 267  * dispatch_block_flags_t is undefined.
 268  *
 269  * @param block
 270  * The block to create the temporary block object from.
 271  */
 272 API_AVAILABLE(macos(10.10), ios(8.0))
 273 DISPATCH_EXPORT DISPATCH_NONNULL2 DISPATCH_NOTHROW
 274 void
 275 dispatch_block_perform(dispatch_block_flags_t flags,
 276                 DISPATCH_NOESCAPE dispatch_block_t block);
 277
 278 /*!
 279  * @function dispatch_block_wait
 280  *
 281  * @abstract
 282  * Wait synchronously until execution of the specified dispatch block object has
 283  * completed or until the specified timeout has elapsed.
 284  *
 285  * @discussion
 286  * This function will return immediately if execution of the block object has
 287  * already completed.
 288  *
 289  * It is not possible to wait for multiple executions of the same block object
 290  * with this interface; use dispatch_group_wait() for that purpose. A single
 291  * dispatch block object may either be waited on once and executed once,
 292  * or it may be executed any number of times. The behavior of any other
 293  * combination is undefined. Submission to a dispatch queue counts as an
 294  * execution, even if cancellation (dispatch_block_cancel) means the block's
 295  * code never runs.
 296  *
 297  * The result of calling this function from multiple threads simultaneously
 298  * with the same dispatch block object is undefined, but note that doing so
 299  * would violate the rules described in the previous paragraph.
 300  *
 301  * If this function returns indicating that the specified timeout has elapsed,
 302  * then that invocation does not count as the one allowed wait.
 303  *
 304  * If at the time this function is called, the specified dispatch block object
 305  * has been submitted directly to a serial queue, the system will make a best
 306  * effort to apply the necessary QOS overrides to ensure that the block and any
 307  * blocks submitted earlier to that serial queue are executed at the QOS class
 308  * (or higher) of the thread calling dispatch_block_wait().
 309  *
 310  * @param block
 311  * The dispatch block object to wait on.
 312  * The result of passing NULL or a block object not returned by one of the
 313  * dispatch_block_create* functions is undefined.
 314  *
 315  * @param timeout
 316  * When to timeout (see dispatch_time). As a convenience, there are the
 317  * DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER constants.
 318  *
 319  * @result
 320  * Returns zero on success (the dispatch block object completed within the
 321  * specified timeout) or non-zero on error (i.e. timed out).
 322  */
 323 API_AVAILABLE(macos(10.10), ios(8.0))
 324 DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NOTHROW
 325 long
 326 dispatch_block_wait(dispatch_block_t block, dispatch_time_t timeout);
 327
 328 /*!
 329  * @function dispatch_block_notify
 330  *
 331  * @abstract
 332  * Schedule a notification block to be submitted to a queue when the execution
 333  * of a specified dispatch block object has completed.
 334  *
 335  * @discussion
 336  * This function will submit the notification block immediately if execution of
 337  * the observed block object has already completed.
 338  *
 339  * It is not possible to be notified of multiple executions of the same block
 340  * object with this interface, use dispatch_group_notify() for that purpose.
 341  *
 342  * A single dispatch block object may either be observed one or more times
 343  * and executed once, or it may be executed any number of times. The behavior
 344  * of any other combination is undefined. Submission to a dispatch queue
 345  * counts as an execution, even if cancellation (dispatch_block_cancel) means
 346  * the block's code never runs.
 347  *
 348  * If multiple notification blocks are scheduled for a single block object,
 349  * there is no defined order in which the notification blocks will be submitted
 350  * to their associated queues.
 351  *
 352  * @param block
 353  * The dispatch block object to observe.
 354  * The result of passing NULL or a block object not returned by one of the
 355  * dispatch_block_create* functions is undefined.
 356  *
 357  * @param queue
 358  * The queue to which the supplied notification block will be submitted when
 359  * the observed block completes.
 360  *
 361  * @param notification_block
 362  * The notification block to submit when the observed block object completes.
 363  */
 364 API_AVAILABLE(macos(10.10), ios(8.0))
 365 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
 366 void
 367 dispatch_block_notify(dispatch_block_t block, dispatch_queue_t queue,
 368                 dispatch_block_t notification_block);
 369
 370 /*!
 371  * @function dispatch_block_cancel
 372  *
 373  * @abstract
 374  * Asynchronously cancel the specified dispatch block object.
 375  *
 376  * @discussion
 377  * Cancellation causes any future execution of the dispatch block object to
 378  * return immediately, but does not affect any execution of the block object
 379  * that is already in progress.
 380  *
 381  * Release of any resources associated with the block object will be delayed
 382  * until execution of the block object is next attempted (or any execution
 383  * already in progress completes).
 384  *
 385  * NOTE: care needs to be taken to ensure that a block object that may be
 386  *       canceled does not capture any resources that require execution of the
 387  *       block body in order to be released (e.g. memory allocated with
 388  *       malloc(3) that the block body calls free(3) on). Such resources will
 389  *       be leaked if the block body is never executed due to cancellation.
 390  *
 391  * @param block
 392  * The dispatch block object to cancel.
 393  * The result of passing NULL or a block object not returned by one of the
 394  * dispatch_block_create* functions is undefined.
 395  */
 396 API_AVAILABLE(macos(10.10), ios(8.0))
 397 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
 398 void
 399 dispatch_block_cancel(dispatch_block_t block);
 400
 401 /*!
 402  * @function dispatch_block_testcancel
 403  *
 404  * @abstract
 405  * Tests whether the given dispatch block object has been canceled.
 406  *
 407  * @param block
 408  * The dispatch block object to test.
 409  * The result of passing NULL or a block object not returned by one of the
 410  * dispatch_block_create* functions is undefined.
 411  *
 412  * @result
 413  * Non-zero if canceled and zero if not canceled.
 414  */
 415 API_AVAILABLE(macos(10.10), ios(8.0))
 416 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_WARN_RESULT DISPATCH_PURE
 417 DISPATCH_NOTHROW
 418 long
 419 dispatch_block_testcancel(dispatch_block_t block);
 420
 421 __END_DECLS
 422
 423 DISPATCH_ASSUME_NONNULL_END
 424
 425 #endif // __BLOCKS__
 426
 427 #endif // __DISPATCH_BLOCK__