private/source_private.h

   1 /*
   2  * Copyright (c) 2008-2013 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 /*
  22  * IMPORTANT: This header file describes INTERNAL interfaces to libdispatch
  23  * which are subject to change in future releases of Mac OS X. Any applications
  24  * relying on these interfaces WILL break.
  25  */
  26
  27 #ifndef __DISPATCH_SOURCE_PRIVATE__
  28 #define __DISPATCH_SOURCE_PRIVATE__
  29
  30 #ifndef __DISPATCH_INDIRECT__
  31 #error "Please #include <dispatch/private.h> instead of this file directly."
  32 #include <dispatch/base.h> // for HeaderDoc
  33 #endif
  34
  35 DISPATCH_ASSUME_NONNULL_BEGIN
  36
  37 __BEGIN_DECLS
  38
  39 /*!
  40  * @const DISPATCH_SOURCE_TYPE_TIMER_WITH_AGGREGATE
  41  * @discussion A dispatch timer source that is part of a timer aggregate.
  42  * The handle is the dispatch timer aggregate object.
  43  * The mask specifies which flags from dispatch_source_timer_flags_t to apply.
  44  */
  45 #define DISPATCH_SOURCE_TYPE_TIMER_WITH_AGGREGATE \
  46                 (&_dispatch_source_type_timer_with_aggregate)
  47 __OSX_AVAILABLE_STARTING(__MAC_10_9,__IPHONE_7_0)
  48 DISPATCH_SOURCE_TYPE_DECL(timer_with_aggregate);
  49
  50 /*!
  51  * @const DISPATCH_SOURCE_TYPE_INTERVAL
  52  * @discussion A dispatch source that submits the event handler block at a
  53  * specified time interval, phase-aligned with all other interval sources on
  54  * the system that have the same interval value.
  55  *
  56  * The initial submission of the event handler will occur at some point during
  57  * the first time interval after the source is created (assuming the source is
  58  * resumed at that time).
  59  *
  60  * By default, the unit for the interval value is milliseconds and the leeway
  61  * (maximum amount of time any individual handler submission may be deferred to
  62  * align with other system activity) for the source is fixed at interval/2.
  63  *
  64  * If the DISPATCH_INTERVAL_UI_ANIMATION flag is specified, the unit for the
  65  * interval value is animation frames (1/60th of a second) and the leeway is
  66  * fixed at one frame.
  67  *
  68  * The handle is the interval value in milliseconds or frames.
  69  * The mask specifies which flags from dispatch_source_timer_flags_t to apply.
  70  */
  71 #define DISPATCH_SOURCE_TYPE_INTERVAL (&_dispatch_source_type_interval)
  72 __OSX_AVAILABLE_STARTING(__MAC_10_9,__IPHONE_7_0)
  73 DISPATCH_SOURCE_TYPE_DECL(interval);
  74
  75 /*!
  76  * @const DISPATCH_SOURCE_TYPE_VFS
  77  * @discussion Apple-internal dispatch source that monitors for vfs events
  78  * defined by dispatch_vfs_flags_t.
  79  * The handle is a process identifier (pid_t).
  80  */
  81 #define DISPATCH_SOURCE_TYPE_VFS (&_dispatch_source_type_vfs)
  82 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0) DISPATCH_LINUX_UNAVAILABLE()
  83 DISPATCH_EXPORT const struct dispatch_source_type_s _dispatch_source_type_vfs;
  84
  85 /*!
  86  * @const DISPATCH_SOURCE_TYPE_VM
  87  * @discussion A dispatch source that monitors virtual memory
  88  * The mask is a mask of desired events from dispatch_source_vm_flags_t.
  89  * This type is deprecated, use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead.
  90  */
  91 #define DISPATCH_SOURCE_TYPE_VM (&_dispatch_source_type_vm)
  92 __OSX_AVAILABLE_BUT_DEPRECATED_MSG(__MAC_10_7, __MAC_10_10, __IPHONE_4_3,
  93                 __IPHONE_8_0, "Use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead")
  94 DISPATCH_LINUX_UNAVAILABLE()
  95 DISPATCH_EXPORT const struct dispatch_source_type_s _dispatch_source_type_vm;
  96
  97 /*!
  98  * @const DISPATCH_SOURCE_TYPE_MEMORYSTATUS
  99  * @discussion A dispatch source that monitors memory status
 100  * The mask is a mask of desired events from
 101  * dispatch_source_memorystatus_flags_t.
 102  */
 103 #define DISPATCH_SOURCE_TYPE_MEMORYSTATUS (&_dispatch_source_type_memorystatus)
 104 __OSX_DEPRECATED(10.9, 10.12, "Use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead")
 105 __IOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead")
 106 __TVOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead")
 107 __WATCHOS_DEPRECATED(1.0, 3.0, "Use DISPATCH_SOURCE_TYPE_MEMORYPRESSURE instead")
 108 DISPATCH_LINUX_UNAVAILABLE()
 109 DISPATCH_EXPORT const struct dispatch_source_type_s
 110                 _dispatch_source_type_memorystatus;
 111
 112 /*!
 113  * @const DISPATCH_SOURCE_TYPE_SOCK
 114  * @discussion A dispatch source that monitors events on socket state changes.
 115  */
 116 #define DISPATCH_SOURCE_TYPE_SOCK (&_dispatch_source_type_sock)
 117 __OSX_AVAILABLE_STARTING(__MAC_10_8, __IPHONE_6_0) DISPATCH_LINUX_UNAVAILABLE()
 118 DISPATCH_EXPORT const struct dispatch_source_type_s _dispatch_source_type_sock;
 119
 120 __END_DECLS
 121
 122 /*!
 123  * @enum dispatch_source_sock_flags_t
 124  *
 125  * @constant DISPATCH_SOCK_CONNRESET
 126  * Received RST
 127  *
 128  * @constant DISPATCH_SOCK_READCLOSED
 129  * Read side is shutdown
 130  *
 131  * @constant DISPATCH_SOCK_WRITECLOSED
 132  * Write side is shutdown
 133  *
 134  * @constant DISPATCH_SOCK_TIMEOUT
 135  * Timeout: rexmt, keep-alive or persist
 136  *
 137  * @constant DISPATCH_SOCK_NOSRCADDR
 138  * Source address not available
 139  *
 140  * @constant DISPATCH_SOCK_IFDENIED
 141  * Interface denied connection
 142  *
 143  * @constant DISPATCH_SOCK_SUSPEND
 144  * Output queue suspended
 145  *
 146  * @constant DISPATCH_SOCK_RESUME
 147  * Output queue resumed
 148  *
 149  * @constant DISPATCH_SOCK_KEEPALIVE
 150  * TCP Keepalive received
 151  *
 152  * @constant DISPATCH_SOCK_CONNECTED
 153  * Socket is connected
 154  *
 155  * @constant DISPATCH_SOCK_DISCONNECTED
 156  * Socket is disconnected
 157  *
 158  * @constant DISPATCH_SOCK_CONNINFO_UPDATED
 159  * Connection info was updated
 160  *
 161  * @constant DISPATCH_SOCK_NOTIFY_ACK
 162  * Notify acknowledgement
 163  */
 164 enum {
 165         DISPATCH_SOCK_CONNRESET = 0x00000001,
 166         DISPATCH_SOCK_READCLOSED = 0x00000002,
 167         DISPATCH_SOCK_WRITECLOSED = 0x00000004,
 168         DISPATCH_SOCK_TIMEOUT = 0x00000008,
 169         DISPATCH_SOCK_NOSRCADDR = 0x00000010,
 170         DISPATCH_SOCK_IFDENIED = 0x00000020,
 171         DISPATCH_SOCK_SUSPEND = 0x00000040,
 172         DISPATCH_SOCK_RESUME = 0x00000080,
 173         DISPATCH_SOCK_KEEPALIVE = 0x00000100,
 174         DISPATCH_SOCK_ADAPTIVE_WTIMO = 0x00000200,
 175         DISPATCH_SOCK_ADAPTIVE_RTIMO = 0x00000400,
 176         DISPATCH_SOCK_CONNECTED = 0x00000800,
 177         DISPATCH_SOCK_DISCONNECTED = 0x00001000,
 178         DISPATCH_SOCK_CONNINFO_UPDATED = 0x00002000,
 179         DISPATCH_SOCK_NOTIFY_ACK = 0x00004000,
 180 };
 181
 182 /*!
 183  * @enum dispatch_source_vfs_flags_t
 184  *
 185  * @constant DISPATCH_VFS_NOTRESP
 186  * Server down.
 187  *
 188  * @constant DISPATCH_VFS_NEEDAUTH
 189  * Server bad auth.
 190  *
 191  * @constant DISPATCH_VFS_LOWDISK
 192  * We're low on space.
 193  *
 194  * @constant DISPATCH_VFS_MOUNT
 195  * New filesystem arrived.
 196  *
 197  * @constant DISPATCH_VFS_UNMOUNT
 198  * Filesystem has left.
 199  *
 200  * @constant DISPATCH_VFS_DEAD
 201  * Filesystem is dead, needs force unmount.
 202  *
 203  * @constant DISPATCH_VFS_ASSIST
 204  * Filesystem needs assistance from external program.
 205  *
 206  * @constant DISPATCH_VFS_NOTRESPLOCK
 207  * Server lockd down.
 208  *
 209  * @constant DISPATCH_VFS_UPDATE
 210  * Filesystem information has changed.
 211  *
 212  * @constant DISPATCH_VFS_VERYLOWDISK
 213  * File system has *very* little disk space left.
 214  *
 215  * @constant DISPATCH_VFS_QUOTA
 216  * We hit a user quota (quotactl) for this filesystem.
 217  *
 218  * @constant DISPATCH_VFS_NEARLOWDISK
 219  * Filesystem is nearly full (below NEARLOWDISK level).
 220  *
 221  * @constant DISPATCH_VFS_DESIREDDISK
 222  * Filesystem has exceeded the DESIREDDISK level
 223  */
 224 enum {
 225         DISPATCH_VFS_NOTRESP = 0x0001,
 226         DISPATCH_VFS_NEEDAUTH = 0x0002,
 227         DISPATCH_VFS_LOWDISK = 0x0004,
 228         DISPATCH_VFS_MOUNT = 0x0008,
 229         DISPATCH_VFS_UNMOUNT = 0x0010,
 230         DISPATCH_VFS_DEAD = 0x0020,
 231         DISPATCH_VFS_ASSIST = 0x0040,
 232         DISPATCH_VFS_NOTRESPLOCK = 0x0080,
 233         DISPATCH_VFS_UPDATE = 0x0100,
 234         DISPATCH_VFS_VERYLOWDISK = 0x0200,
 235         DISPATCH_VFS_QUOTA = 0x1000,
 236         DISPATCH_VFS_NEARLOWDISK = 0x2000,
 237         DISPATCH_VFS_DESIREDDISK = 0x4000,
 238 };
 239
 240 /*!
 241  * @enum dispatch_source_timer_flags_t
 242  *
 243  * @constant DISPATCH_TIMER_BACKGROUND
 244  * Specifies that the timer is used to trigger low priority maintenance-level
 245  * activity and that the system may apply larger minimum leeway values to the
 246  * timer in order to align it with other system activity.
 247  *
 248  * @constant DISPATCH_INTERVAL_UI_ANIMATION
 249  * Specifies that the interval source is used for UI animation. The unit for
 250  * the interval value of such sources is frames (1/60th of a second) and the
 251  * leeway is fixed at one frame.
 252  */
 253 enum {
 254         DISPATCH_TIMER_BACKGROUND = 0x2,
 255         DISPATCH_INTERVAL_UI_ANIMATION = 0x20,
 256 };
 257
 258 /*!
 259  * @enum dispatch_source_mach_send_flags_t
 260  *
 261  * @constant DISPATCH_MACH_SEND_POSSIBLE
 262  * The mach port corresponding to the given send right has space available
 263  * for messages. Delivered only once a mach_msg() to that send right with
 264  * options MACH_SEND_MSG|MACH_SEND_TIMEOUT|MACH_SEND_NOTIFY has returned
 265  * MACH_SEND_TIMED_OUT (and not again until the next such mach_msg() timeout).
 266  * NOTE: The source must have registered the send right for monitoring with the
 267  *       system for such a mach_msg() to arm the send-possible notifcation, so
 268  *       the initial send attempt must occur from a source registration handler.
 269  */
 270 enum {
 271         DISPATCH_MACH_SEND_POSSIBLE = 0x8,
 272 };
 273
 274 /*!
 275  * @enum dispatch_source_proc_flags_t
 276  *
 277  * @constant DISPATCH_PROC_REAP
 278  * The process has been reaped by the parent process via wait*().
 279  * This flag is deprecated and will be removed in a future release.
 280  */
 281 enum {
 282         DISPATCH_PROC_REAP __OSX_AVAILABLE_BUT_DEPRECATED(
 283                         __MAC_10_6, __MAC_10_9, __IPHONE_4_0, __IPHONE_7_0) = 0x10000000,
 284 };
 285
 286 /*!
 287  * @enum dispatch_source_vm_flags_t
 288  *
 289  * @constant DISPATCH_VM_PRESSURE
 290  * The VM has experienced memory pressure.
 291  */
 292
 293 enum {
 294         DISPATCH_VM_PRESSURE __OSX_AVAILABLE_BUT_DEPRECATED_MSG(
 295                         __MAC_10_7, __MAC_10_10, __IPHONE_4_3, __IPHONE_8_0,
 296                         "Use DISPATCH_MEMORYPRESSURE_WARN instead") = 0x80000000,
 297 };
 298
 299 /*!
 300  * @typedef dispatch_source_memorypressure_flags_t
 301  * Type of dispatch_source_memorypressure flags
 302  *
 303  * @constant DISPATCH_MEMORYPRESSURE_LOW_SWAP
 304  * The system's memory pressure state has entered the "low swap" condition.
 305  * Restricted to the root user.
 306  */
 307 enum {
 308         DISPATCH_MEMORYPRESSURE_LOW_SWAP
 309                         __OSX_AVAILABLE_STARTING(__MAC_10_10, __IPHONE_8_0) = 0x08,
 310 };
 311
 312 /*!
 313  * @enum dispatch_source_memorystatus_flags_t
 314  * @warning Deprecated, see DISPATCH_MEMORYPRESSURE_*
 315  */
 316 enum {
 317         DISPATCH_MEMORYSTATUS_PRESSURE_NORMAL
 318                         __OSX_DEPRECATED(10.9, 10.12, "Use DISPATCH_MEMORYPRESSURE_NORMAL instead")
 319                         __IOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_NORMAL instead")
 320                         __TVOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_NORMAL instead")
 321                         __WATCHOS_DEPRECATED(1.0, 3.0, "Use DISPATCH_MEMORYPRESSURE_NORMAL instead")
 322                         = 0x01,
 323         DISPATCH_MEMORYSTATUS_PRESSURE_WARN
 324                         __OSX_DEPRECATED(10.9, 10.12, "Use DISPATCH_MEMORYPRESSURE_WARN instead")
 325                         __IOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_WARN instead")
 326                         __TVOS_DEPRECATED(6.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_WARN instead")
 327                         __WATCHOS_DEPRECATED(1.0, 3.0, "Use DISPATCH_MEMORYPRESSURE_WARN instead")
 328                         = 0x02,
 329         DISPATCH_MEMORYSTATUS_PRESSURE_CRITICAL
 330                         __OSX_DEPRECATED(10.9, 10.12, "Use DISPATCH_MEMORYPRESSURE_CRITICAL instead")
 331                         __IOS_DEPRECATED(8.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_CRITICAL instead")
 332                         __TVOS_DEPRECATED(8.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_CRITICAL instead")
 333                         __WATCHOS_DEPRECATED(1.0, 3.0, "Use DISPATCH_MEMORYPRESSURE_CRITICAL instead")
 334                         = 0x04,
 335         DISPATCH_MEMORYSTATUS_LOW_SWAP
 336                         __OSX_DEPRECATED(10.10, 10.12, "Use DISPATCH_MEMORYPRESSURE_LOW_SWAP instead")
 337                         __IOS_DEPRECATED(8.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_LOW_SWAP instead")
 338                         __TVOS_DEPRECATED(8.0, 10.0, "Use DISPATCH_MEMORYPRESSURE_LOW_SWAP instead")
 339                         __WATCHOS_DEPRECATED(1.0, 3.0, "Use DISPATCH_MEMORYPRESSURE_LOW_SWAP instead")
 340                         = 0x08,
 341 };
 342
 343 /*!
 344  * @typedef dispatch_source_memorypressure_flags_t
 345  * Type of dispatch_source_memorypressure flags
 346  *
 347  * @constant DISPATCH_MEMORYPRESSURE_PROC_LIMIT_WARN
 348  * The memory of the process has crossed 80% of its high watermark limit.
 349  *
 350  * @constant DISPATCH_MEMORYPRESSURE_PROC_LIMIT_CRITICAL
 351  * The memory of the process has reached 100% of its high watermark limit.
 352  */
 353 enum {
 354         DISPATCH_MEMORYPRESSURE_PROC_LIMIT_WARN
 355                         __OSX_AVAILABLE(10.12) __IOS_AVAILABLE(10.10)
 356                         __TVOS_AVAILABLE(10.10) __WATCHOS_AVAILABLE(3.0) = 0x10,
 357
 358         DISPATCH_MEMORYPRESSURE_PROC_LIMIT_CRITICAL
 359                 __OSX_AVAILABLE(10.12) __IOS_AVAILABLE(10.10)
 360                 __TVOS_AVAILABLE(10.10) __WATCHOS_AVAILABLE(3.0) = 0x20,
 361 };
 362
 363
 364 __BEGIN_DECLS
 365
 366 /*!
 367  * @function dispatch_source_cancel_and_wait
 368  *
 369  * @abstract
 370  * Synchronously cancel the dispatch source, preventing any further invocation
 371  * of its event handler block.
 372  *
 373  * @discussion
 374  * Cancellation prevents any further invocation of handler blocks for the
 375  * specified dispatch source, but does not interrupt a handler block that is
 376  * already in progress.
 377  *
 378  * When this function returns, any handler block that may have been in progress
 379  * has returned, the specified source has been unregistered and it is safe to
 380  * reclaim any system resource (such as file descriptors or mach ports) that
 381  * the specified source was monitoring.
 382  *
 383  * If the specified dispatch source is inactive, it will be activated as a side
 384  * effect of calling this function.
 385  *
 386  * It is possible to call this function from several threads concurrently,
 387  * and it is the responsibility of the callers to synchronize reclaiming the
 388  * associated system resources.
 389  *
 390  * This function is not subject to priority inversion when it is waiting on
 391  * a handler block still in progress, unlike patterns based on waiting on
 392  * a dispatch semaphore or a dispatch group signaled (or left) from the source
 393  * cancel handler.
 394  *
 395  * This function must not be called if the specified source has a cancel
 396  * handler set, or from the context of its handler blocks.
 397  *
 398  * This function must not be called from the context of the target queue of
 399  * the specified source or from any queue that synchronizes with it. Note that
 400  * calling dispatch_source_cancel() from such a context already guarantees
 401  * that no handler is in progress, and that no new event will be delivered.
 402  *
 403  * This function must not be called on sources suspended with an explicit
 404  * call to dispatch_suspend(), or being concurrently activated on another
 405  * thread.
 406  *
 407  * @param source
 408  * The dispatch source to be canceled.
 409  * The result of passing NULL in this parameter is undefined.
 410  */
 411 __OSX_AVAILABLE(10.12) __IOS_AVAILABLE(10.10)
 412 __TVOS_AVAILABLE(10.10) __WATCHOS_AVAILABLE(3.0)
 413 DISPATCH_EXPORT DISPATCH_NOTHROW
 414 void
 415 dispatch_source_cancel_and_wait(dispatch_source_t source);
 416
 417 /*!
 418  * @typedef dispatch_timer_aggregate_t
 419  *
 420  * @abstract
 421  * Dispatch timer aggregates are sets of related timers.
 422  */
 423 DISPATCH_DECL(dispatch_timer_aggregate);
 424
 425 /*!
 426  * @function dispatch_timer_aggregate_create
 427  *
 428  * @abstract
 429  * Creates a new dispatch timer aggregate.
 430  *
 431  * @discussion
 432  * A dispatch timer aggregate is a set of related timers whose overall timing
 433  * parameters can be queried.
 434  *
 435  * Timers are added to an aggregate when a timer source is created with type
 436  * DISPATCH_SOURCE_TYPE_TIMER_WITH_AGGREGATE.
 437  *
 438  * @result
 439  * The newly created dispatch timer aggregate.
 440  */
 441 __OSX_AVAILABLE_STARTING(__MAC_10_9,__IPHONE_7_0)
 442 DISPATCH_EXPORT DISPATCH_MALLOC DISPATCH_RETURNS_RETAINED DISPATCH_WARN_RESULT
 443 DISPATCH_NOTHROW
 444 dispatch_timer_aggregate_t
 445 dispatch_timer_aggregate_create(void);
 446
 447 /*!
 448  * @function dispatch_timer_aggregate_get_delay
 449  *
 450  * @abstract
 451  * Retrieves the delay until a timer in the given aggregate will next fire.
 452  *
 453  * @param aggregate
 454  * The dispatch timer aggregate to query.
 455  *
 456  * @param leeway_ptr
 457  * Optional pointer to a variable filled with the leeway (in ns) that will be
 458  * applied to the return value. May be NULL.
 459  *
 460  * @result
 461  * Delay in ns from now.
 462  */
 463 __OSX_AVAILABLE_STARTING(__MAC_10_9,__IPHONE_7_0)
 464 DISPATCH_EXPORT DISPATCH_NOTHROW
 465 uint64_t
 466 dispatch_timer_aggregate_get_delay(dispatch_timer_aggregate_t aggregate,
 467                 uint64_t *_Nullable leeway_ptr);
 468
 469 #if __has_include(<mach/mach.h>)
 470 /*!
 471  * @typedef dispatch_mig_callback_t
 472  *
 473  * @abstract
 474  * The signature of a function that handles Mach message delivery and response.
 475  */
 476 typedef boolean_t (*dispatch_mig_callback_t)(mach_msg_header_t *message,
 477                 mach_msg_header_t *reply);
 478
 479 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0) DISPATCH_LINUX_UNAVAILABLE()
 480 DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
 481 mach_msg_return_t
 482 dispatch_mig_server(dispatch_source_t ds, size_t maxmsgsz,
 483                 dispatch_mig_callback_t callback);
 484
 485 /*!
 486  * @function dispatch_mach_msg_get_context
 487  *
 488  * @abstract
 489  * Extract the context pointer from a mach message trailer.
 490  */
 491 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0) DISPATCH_LINUX_UNAVAILABLE()
 492 DISPATCH_EXPORT DISPATCH_PURE DISPATCH_WARN_RESULT DISPATCH_NONNULL_ALL
 493 DISPATCH_NOTHROW
 494 void *_Nullable
 495 dispatch_mach_msg_get_context(mach_msg_header_t *msg);
 496 #endif
 497
 498 __END_DECLS
 499
 500 DISPATCH_ASSUME_NONNULL_END
 501
 502 #endif