2 * UCW Library -- Main Loop
4 * (c) 2004--2011 Martin Mares <mj@ucw.cz>
6 * This software may be freely distributed and used according to the terms
7 * of the GNU Lesser General Public License.
10 #ifndef _UCW_MAINLOOP_H
11 #define _UCW_MAINLOOP_H
13 #include "ucw/clists.h"
22 * First of all, let us take a look at the basic operations with main loop contexts.
25 /** The main loop context **/
27 timestamp_t now; /* [*] Current time in milliseconds since the UNIX epoch. See main_get_time(). */
28 ucw_time_t now_seconds; /* [*] Current time in seconds since the epoch. */
29 timestamp_t idle_time; /* [*] Total time in milliseconds spent by waiting for events. */
30 uns shutdown; /* [*] Setting this to nonzero forces the main_loop() function to terminate. */
32 clist file_active_list;
39 #ifdef CONFIG_UCW_EPOLL
40 int epoll_fd; /* File descriptor used for epoll */
41 struct epoll_event *epoll_events;
42 clist file_recalc_list;
44 uns poll_table_obsolete;
45 struct pollfd *poll_table;
46 struct main_file **poll_file_table;
48 struct main_timer **timer_table; /* Growing array containing the heap of timers */
49 sigset_t want_signals;
52 struct main_file *sig_pipe_file;
53 struct main_signal *sigchld_handler;
56 struct main_context *main_new(void); /** Create a new context. **/
59 * Delete a context, assuming it does have any event handlers attached. Does nothing if @m is NULL.
60 * It is allowed to call @main_delete() from a hook function of the same context, but you must
61 * never return to the main loop -- e.g., you can exit() the process instead.
63 void main_delete(struct main_context *m);
66 * Delete a context. If there are any event handlers attached, they are deactivated
67 * (but the responsibility to free the memory there were allocated from lies upon you).
68 * If there are any file handlers, the corresponding file descriptors are closed.
70 void main_destroy(struct main_context *m);
72 /** Switch the current context of the calling thread. Returns the previous current context. **/
73 struct main_context *main_switch_context(struct main_context *m);
75 /** Return the current context. Dies if there is none or if the context has been deleted. **/
76 struct main_context *main_current(void);
78 /** Initialize the main loop module and create a top-level context. **/
81 /** Deinitialize the main loop module, calling @main_delete() on the top-level context. **/
82 void main_cleanup(void);
85 * Deinitialize the main loop module, calling @main_destroy() on the top-level context.
86 * This is especially useful in a freshly forked-off child process.
88 void main_teardown(void);
91 * Start the event loop on the current context.
92 * It will watch the provided objects and call callbacks.
93 * Terminates when someone calls @main_shut_down(),
94 * or when all <<hook,hooks>> return <<enum_main_hook_return,`HOOK_DONE`>>
95 * or at last one <<hook,hook>> returns <<enum_main_hook_return,`HOOK_SHUTDOWN`>>.
100 * Perform a single iteration of the main loop.
101 * Check if there are any events ready and process them.
102 * If there are none, do not wait.
104 void main_step(void);
106 /** Ask the main loop to terminate at the nearest occasion. **/
107 static inline void main_shut_down(void)
109 main_current()->shutdown = 1;
113 * Show the current state of a given context (use @main_debug() for the current context).
114 * Available only if LibUCW has been compiled with `CONFIG_DEBUG`.
116 void main_debug_context(struct main_context *m);
121 main_debug_context(main_current());
129 * The event loop provides the current time, measured as a 64-bit number
130 * of milliseconds since the system epoch (represented in the type `timestamp_t`).
132 * You can also register timers, which call a handler function at a given moment.
133 * The handler function must either call @timer_del() to delete the timer, or call
134 * @timer_add() with a different expiration time.
138 * Get the current timestamp cached in the current context. It is refreshed in every
139 * iteration of the event loop, or explicitly by calling @main_get_time().
141 static inline timestamp_t main_get_now(void)
143 return main_current()->now;
146 /** An analog of @main_get_now() returning the number of seconds since the system epoch. **/
147 static inline ucw_time_t main_get_now_seconds(void)
149 return main_current()->now_seconds;
153 * This is a description of a timer.
154 * You define the handler function and possibly user-defined data you wish
155 * to pass to the handler, and then you invoke @timer_add().
161 void (*handler)(struct main_timer *tm); /* [*] Function to be called when the timer expires. */
162 void *data; /* [*] Data for use by the handler */
166 * Add a new timer into the main loop to be watched and called
167 * when it expires. It can also be used to modify an already running
168 * timer. It is permitted (and usual) to call this function from the
169 * timer's handler itself if you want the timer to trigger again.
171 * The @expire parameter is absolute, use @timer_add_rel() for a relative version.
173 void timer_add(struct main_timer *tm, timestamp_t expires);
175 /** Like @timer_add(), but the expiration time is relative to the current time. **/
176 void timer_add_rel(struct main_timer *tm, timestamp_t expires_delta);
179 * Removes a timer from the active ones. It is permitted (and common) to call
180 * this function from the timer's handler itself if you want to deactivate
183 void timer_del(struct main_timer *tm);
186 * Forces refresh of the current timestamp cached in the active context.
187 * You usually do not need to call this, since it is called every time the
188 * loop polls for events. It is here if you need extra precision or some of the
189 * hooks takes a long time.
191 void main_get_time(void);
193 /** Show current state of a timer. Available only if LibUCW has been compiled with `CONFIG_DEBUG`. **/
194 void timer_debug(struct main_timer *tm);
198 * Activity on file descriptors
199 * ----------------------------
201 * You can ask the main loop to watch a set of file descriptors for activity.
202 * (This is a generalization of the select() and poll() system calls. Internally,
203 * it uses either poll() or the more efficient epoll().)
205 * You create a <<struct_main_file,`struct main_file`>>, fill in a file descriptor
206 * and pointers to handler functions to be called when the descriptor becomes
207 * ready for reading and/or writing, and call @file_add(). When you need to
208 * modify the handlers (e.g., to set them to NULL if you are no longer interested
209 * in a given event), you should call @file_chg() to notify the main loop about
212 * From within the handler functions, you are allowed to call @file_chg() and even
215 * The return value of a handler function should be either <<enum_main_hook_return,`HOOK_RETRY`>>
216 * or <<enum_main_hook_return,`HOOK_IDLE`>>. <<enum_main_hook_return,`HOOK_RETRY`>>
217 * signals that the function would like to consume more data immediately
218 * (i.e., it wants to be called again soon, but the event loop can postpone it after
219 * processing other events to avoid starvation). <<enum_main_hook_return,`HOOK_IDLE`>>
220 * tells that the handler wants to be called when the descriptor becomes ready again.
222 * For backward compatibility, 0 can be used instead of <<enum_main_hook_return,`HOOK_IDLE`>>
223 * and 1 for <<enum_main_hook_return,`HOOK_RETRY`>>.
225 * If you want to read/write fixed-size blocks of data asynchronously, the
226 * <<blockio,Asynchronous block I/O>> interface could be more convenient.
230 * This structure describes a file descriptor to be watched and the handlers
231 * to be called when the descriptor is ready for reading and/or writing.
235 int fd; /* [*] File descriptor */
236 int (*read_handler)(struct main_file *fi); /* [*] To be called when ready for reading/writing; must call file_chg() afterwards */
237 int (*write_handler)(struct main_file *fi);
238 void *data; /* [*] Data for use by the handlers */
240 #ifdef CONFIG_UCW_EPOLL
241 uns last_want_events;
243 struct pollfd *pollfd;
248 * Insert a <<struct_main_file,`main_file`>> structure into the main loop to be
249 * watched for activity. You can call this at any time, even inside a handler
250 * (of course for a different file descriptor than the one of the handler).
252 * The file descriptor is automatically set to the non-blocking mode.
254 void file_add(struct main_file *fi);
257 * Tell the main loop that the file structure has changed. Call it whenever you
258 * change any of the handlers.
260 * Can be called only on active files (only the ones added by @file_add()).
262 void file_chg(struct main_file *fi);
265 * Removes a file from the watched set. If you want to close a descriptor,
266 * please use this function first.
268 * Can be called from a handler.
270 void file_del(struct main_file *fi);
272 /** Show current state of a file. Available only if LibUCW has been compiled with `CONFIG_DEBUG`. **/
273 void file_debug(struct main_file *fi);
277 * Asynchronous block I/O
278 * ----------------------
280 * If you are reading or writing fixed-size blocks of data, you can let the
281 * block I/O interface handle the boring routine of handling partial reads
282 * and writes for you.
284 * You just create <<struct_main_block_io,`struct main_block_io`>> and call
285 * @block_io_add() on it, which sets up some <<struct_main_file,`main_file`>>s internally.
286 * Then you can just call @block_io_read() or @block_io_write() to ask for
287 * reading or writing of a given block. When the operation is finished,
288 * your handler function is called.
290 * Additionally, the block I/O is equipped with a timer, which can be used
291 * to detect communication timeouts. The timer is not touched internally
292 * (except that it gets added and deleted at the right places), feel free
293 * to adjust it from your handler functions by @block_io_set_timeout().
294 * When the timer expires, the error handler is automatically called with
295 * <<enum_block_io_err_cause,`BIO_ERR_TIMEOUT`>>.
298 /** The block I/O structure. **/
299 struct main_block_io {
300 struct main_file file;
301 byte *rbuf; /* Read/write pointers for use by file_read/write */
305 void (*read_done)(struct main_block_io *bio); /* [*] Called when file_read is finished; rpos < rlen if EOF */
306 void (*write_done)(struct main_block_io *bio); /* [*] Called when file_write is finished */
307 void (*error_handler)(struct main_block_io *bio, int cause); /* [*] Handler to call on errors */
308 struct main_timer timer;
309 void *data; /* [*] Data for use by the handlers */
312 /** Activate a block I/O structure. **/
313 void block_io_add(struct main_block_io *bio, int fd);
315 /** Deactivate a block I/O structure. **/
316 void block_io_del(struct main_block_io *bio);
319 * Specifies when or why an error happened. This is passed to the error handler.
320 * `errno` is still set to the original source of error. The only exception
321 * is `BIO_ERR_TIMEOUT`, in which case `errno` is not set and the only possible
322 * cause of it is timeout of the timer associated with the block_io
323 * (see @block_io_set_timeout()).
325 enum block_io_err_cause {
332 * Ask the main loop to read @len bytes of data from @bio into @buf.
333 * It cancels any previous unfinished read requested in this way.
335 * When the read is done, the read_done() handler is called. If an EOF occurred,
336 * `rpos < rlen` (eg. not all data were read).
338 * Can be called from a handler.
340 * You can use a call with zero @len to cancel the current read, but all read data
341 * will be thrown away.
343 void block_io_read(struct main_block_io *bio, void *buf, uns len);
346 * Request that the main loop writes @len bytes of data from @buf to @bio.
347 * Cancels any previous unfinished write and overwrites `write_handler`.
349 * When it is written, the write_done() handler is called.
351 * Can be called from a handler.
353 * If you call it with zero @len, it will cancel the previous write, but note
354 * that some data may already be written.
356 void block_io_write(struct main_block_io *bio, void *buf, uns len);
359 * Sets a timer for a file @bio. If the timer is not overwritten or disabled
360 * until @expires_delta milliseconds, the file timeouts and error_handler() is called with
361 * <<enum_block_io_err_cause,`BIO_ERR_TIMEOUT`>>. A value of `0` stops the timer.
363 * Previous setting of the timeout on the same file will be overwritten.
365 * The use-cases for this are mainly sockets or pipes, when:
367 * - You want to drop inactive connections (no data comes in or out for a given time, not
368 * incomplete messages).
369 * - You want to enforce answer in a given time (for example authentication).
370 * - Watching maximum time for a whole connection.
372 void block_io_set_timeout(struct main_block_io *bio, timestamp_t expires_delta);
376 * Asynchronous record I/O
377 * -----------------------
379 * Record-based I/O is another front-end to the main loop file operations.
380 * Unlike its older cousin `main_block_io`, it is able to process records
381 * of variable length.
383 * To set it up, you create <<struct_main_rec_io,`struct main_rec_io`>> and call
384 * @rec_io_add() on it, which sets up some <<struct_main_file,`main_file`>>s internally.
386 * To read data from the file, call @rec_io_start_read() first. Whenever any data
387 * arrive from the file, they are appended to an internal buffer and the `read_handler`
388 * hook is called. The hook checks if the buffer already contains a complete record.
389 * If it is so, it processes the record and returns the number of bytes consumed.
390 * Otherwise, it returns 0 to tell the buffering machinery that more data are needed.
391 * When the read handler decides to destroy the `main_rec_io`, it must return `~0U`.
393 * On the write side, `main_rec_io` maintains a buffer keeping all data that should
394 * be written to the file. The @rec_io_write() function appends data to this buffer
395 * and it is written on background. A simple flow-control mechanism can be asked
396 * for: when more than `write_throttle_read` data are buffered for writing, reading
397 * is temporarily suspended.
399 * Additionally, the record I/O is equipped with a timer, which can be used
400 * to detect communication timeouts. The timer is not touched internally
401 * (except that it gets added and deleted at the right places), feel free
402 * to adjust it from your handler functions by @rec_io_set_timeout().
404 * All important events are passed to the `notify_handler`: errors when
405 * reading or writing, timeouts, the write buffer becoming empty, ... See
406 * <<enum_rec_io_notify_status,`enum rec_io_notify_status`>> for a complete list.
409 /** The record I/O structure. **/
411 struct main_file file;
413 byte *read_rec_start; /* [*] Start of current record */
414 uns read_avail; /* [*] How much data is available */
415 uns read_prev_avail; /* [*] How much data was available in previous read_handler */
416 uns read_buf_size; /* [*] Read buffer size allocated (can be set before rec_io_add()) */
417 uns read_started; /* Reading requested by user */
418 uns read_running; /* Reading really runs (read_started && not stopped by write_throttle_read) */
419 uns read_rec_max; /* [*] Maximum record size (0=unlimited) */
420 clist busy_write_buffers;
421 clist idle_write_buffers;
422 uns write_buf_size; /* [*] Write buffer size allocated (can be set before rec_io_add()) */
423 uns write_watermark; /* [*] How much data are waiting to be written */
424 uns write_throttle_read; /* [*] If more than write_throttle_read bytes are buffered, stop reading; 0=no stopping */
425 uns (*read_handler)(struct main_rec_io *rio); /* [*] Called whenever more bytes are read; returns 0 (want more) or number of bytes eaten */
426 int (*notify_handler)(struct main_rec_io *rio, int status); /* [*] Called to notify about errors and other events */
427 /* Returns either HOOK_RETRY or HOOK_IDLE. */
428 struct main_timer timer;
429 void *data; /* [*] Data for use by the handlers */
432 /** Activate a record I/O structure. **/
433 void rec_io_add(struct main_rec_io *rio, int fd);
435 /** Deactivate a record I/O structure. **/
436 void rec_io_del(struct main_rec_io *rio);
438 /** Start reading. **/
439 void rec_io_start_read(struct main_rec_io *rio);
441 /** Stop reading. **/
442 void rec_io_stop_read(struct main_rec_io *rio);
444 /** Analogous to @block_io_set_timeout(). **/
445 void rec_io_set_timeout(struct main_rec_io *bio, timestamp_t expires_delta);
447 void rec_io_write(struct main_rec_io *rio, void *data, uns len);
450 * An auxiliary function used for parsing of lines. When called in the @read_handler,
451 * it searches for the end of line character. When a complete line is found, the length
452 * of the line (including the end of line character) is returned. Otherwise, it returns zero.
454 uns rec_io_parse_line(struct main_rec_io *rio);
457 * Specifies what kind of error or other event happened, when the @notify_handler
458 * is called. In case of I/O errors, `errno` is still set.
460 * Upon @RIO_ERR_READ, @RIO_ERR_RECORD_TOO_LARGE and @RIO_EVENT_EOF, reading is stopped
461 * automatically. Upon @RIO_ERR_WRITE, writing is stopped. Upon @RIO_ERR_TIMEOUT, only the
462 * timer is deactivated.
464 * In all cases, the notification handler is allowed to call @rec_io_del(), but it
465 * must return @HOOK_IDLE in such cases.
467 enum rec_io_notify_status {
468 RIO_ERR_READ = -1, /* read() returned an error, errno set */
469 RIO_ERR_WRITE = -2, /* write() returned an error, errno set */
470 RIO_ERR_TIMEOUT = -3, /* A timeout has occurred */
471 RIO_ERR_RECORD_TOO_LARGE = -4, /* Read: read_rec_max has been exceeded */
472 RIO_EVENT_ALL_WRITTEN = 1, /* All buffered data has been written */
473 RIO_EVENT_PART_WRITTEN = 2, /* Some buffered data has been written, but more remains */
474 RIO_EVENT_EOF = 3, /* Read: EOF seen */
482 * The hooks are called whenever the main loop performs an iteration.
483 * You can shutdown the main loop from within them or request an iteration
484 * to happen without sleeping (just poll, no waiting for events).
488 * A hook. It contains the function to call and some user data.
490 * The handler() must return one value from
491 * <<enum_main_hook_return,`main_hook_return`>>.
493 * Fill with the hook and data and pass it to @hook_add().
497 int (*handler)(struct main_hook *ho); /* [*] Hook function; returns HOOK_xxx */
498 void *data; /* [*] For use by the handler */
502 * Return value of the hook handler().
503 * Specifies what should happen next.
505 * - `HOOK_IDLE` -- Let the loop sleep until something happens, call after that.
506 * - `HOOK_RETRY` -- Force the loop to perform another iteration without sleeping.
507 * This will cause calling of all the hooks again soon.
508 * - `HOOK_DONE` -- The loop will terminate if all hooks return this.
509 * - `HOOK_SHUTDOWN` -- Shuts down the loop.
511 * The `HOOK_IDLE` and `HOOK_RETRY` constants are also used as return values
514 enum main_hook_return {
522 * Inserts a new hook into the loop.
523 * The hook will be scheduled at least once before next sleep.
524 * May be called from inside a hook handler too.
526 void hook_add(struct main_hook *ho);
529 * Removes an existing hook from the loop.
530 * May be called from inside a hook handler (to delete itself or another hook).
532 void hook_del(struct main_hook *ho);
534 /** Show current state of a hook. Available only if LibUCW has been compiled with `CONFIG_DEBUG`. **/
535 void hook_debug(struct main_hook *ho);
542 * The main loop can watch child processes and notify you,
543 * when some of them terminates.
547 * Description of a watched process.
548 * You fill in the handler() and `data`.
549 * The rest is set with @process_fork().
551 struct main_process {
553 int pid; /* Process id (0=not running) */
554 int status; /* Exit status (-1=fork failed) */
555 char status_msg[EXIT_STATUS_MSG_SIZE];
556 void (*handler)(struct main_process *mp); /* [*] Called when the process exits; process_del done automatically */
557 void *data; /* [*] For use by the handler */
561 * Asks the main loop to watch this process.
562 * As it is done automatically in @process_fork(), you need this only
563 * if you removed the process previously by @process_del().
565 void process_add(struct main_process *mp);
568 * Removes the process from the watched set. This is done
569 * automatically, when the process terminates, so you need it only
570 * when you do not want to watch a running process any more.
572 void process_del(struct main_process *mp);
575 * Forks and fills the @mp with information about the new process.
577 * If the fork() succeeds, it:
579 * - Returns 0 in the child.
580 * - Returns 1 in the parent and calls @process_add() on it.
582 * In the case of unsuccessful fork(), it:
584 * - Fills in the `status_msg` and sets `status` to -1.
585 * - Calls the handler() as if the process terminated.
588 int process_fork(struct main_process *mp);
590 /** Show current state of a process. Available only if LibUCW has been compiled with `CONFIG_DEBUG`. **/
591 void process_debug(struct main_process *pr);
595 * Synchronous delivery of signals
596 * -------------------------------
598 * UNIX signals are delivered to processes in an asynchronous way: when a signal
599 * arrives (and it is not blocked), the process is interrupted and the corresponding
600 * signal handler function is called. However, most data structures and even most
601 * system library calls are not safe with respect to interrupts, so most program
602 * using signals contain subtle race conditions and may fail once in a long while.
604 * To avoid this problem, the event loop can be asked for synchronous delivery
605 * of signals. When a signal registered with @signal_add() arrives, it wakes up
606 * the loop (if it is not already awake) and it is processed in the same way
607 * as all other events.
609 * When used in a multi-threaded program, the signals are delivered to the thread
610 * which is currently using the particular main loop context. If the context is not
611 * current in any thread, the signals are blocked.
613 * As usually with UNIX signals, multiple instances of a single signal can be
614 * merged and delivered only once. (Some implementations of the main loop can even
615 * drop a signal completely during very intensive signal traffic, when an internal
616 * signal queue overflows.)
619 /** Description of a signal to catch. **/
622 int signum; /* [*] Signal to catch */
623 void (*handler)(struct main_signal *ms); /* [*] Called when the signal arrives */
624 void *data; /* [*] For use by the handler */
627 /** Request a signal to be caught and delivered synchronously. **/
628 void signal_add(struct main_signal *ms);
630 /** Cancel a request for signal catching. **/
631 void signal_del(struct main_signal *ms);
633 /** Show current state of a signal catcher. Available only if LibUCW has been compiled with `CONFIG_DEBUG`. **/
634 void signal_debug(struct main_signal *sg);