mirror of
https://github.com/libevent/libevent.git
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1af8017648
The sizeof `struct event` can reduced on both 32 bit and 64 bit systems
by moving the 4 bytes that make up `ev_events` and `ev_res` below `ev_fd`,
before `struct event_base * ev_base;` since our compiler wouldn't dare do
such a thing (it instead will pad twice, whereas it only needs to be padded
once)
```C
struct event {
/* OFFS | SZ Bytes | Total Bytes | START - END */
struct event_callback ev_evcallback; /* 0x0 | 40 | 40 | 0x0 - 0x28 */
union { /* 0x28 | ----------- | ----------- | ------------ */
TAILQ_ENTRY(event) ev_next_with_common_timeout; /* | ((16)) | | */
int min_heap_idx; /* | ((04)) | | */
} ev_timeout_pos; /* | 16 | 56 | 0x28 - 0x38 */
int ev_fd; /* 0x38 | 04 | 60 | 0x38 - 0x3c */
```
Since the next field is 8 bytes in length, and we are up to 60 bytes, `ev_fd` ends up being padded (4 more bytes on 64b).
```C
/* --- 1 byte gap HERE ---> 1 | <61> */
/* --- 1 byte gap HERE ---> 1 | <62> */
/* --- 1 byte gap HERE ---> 1 | <63> */
/* --- 1 byte gap HERE ---> 1 | <64> */
struct event_base * ev_base; /* 0x3c | 8 | 68 | 0x3c - 0x40 */
union { /* 0x40 | ------------ | ---------- | ------------ */
struct { /* | ------------ | | */
LIST_ENTRY (event) ev_io_next; /* | ((16+ | | */
struct timeval ev_timeout; /* | 16)) | | */
} ev_io; /* | ((32)) | | */
struct { /* | ------------ | | */
LIST_ENTRY (event) ev_signal_next; /* | ((16+ | | */
short ev_ncalls; /* | 02+ | | */
short * ev_pncalls; /* | 08)) | | */
} ev_signal; /* | ((26)) | | */
} ev_; /* 0x60 | 32 | 100 | 0x40 - 0x60 */
short ev_events; /* 0x60 | 2 | 102 | 0x60 - 0x62 */
short ev_res; /* 0x62 | 2 | 104 | 0x62 - 0x64 */
```
We now hit another line, `struct timeval` is 16 bytes on 64b arch, so we have 4 more bytes
of padding on `ev_res`.
```C
/* --- 1 byte gap HERE --- */
/* --- 1 byte gap HERE --- */
/* --- 1 byte gap HERE --- */
/* --- 1 byte gap HERE --- */
struct timeval ev_timeout; /* 0x64 | 16 | 120 | 0x64 - 0x74 */
};
```
After moving `ev_events` and `ev_res` below `ev_fd` we have something
a bit more optimal:
```C
struct event2 {
/* OFFS | SZ / Bytes | RSUM Bytes | START - END */
struct event_callback ev_evcallback; /* 0x0 | 40 | 40 | 0x0 - 0x28 */
union { /* 0x28 | ------------ | ---------- | ------------ */
TAILQ_ENTRY(event) ev_next_with_common_timeout; /* | ((16)) | | */
int min_heap_idx; /* | ((04)) | | */
} ev_timeout_pos; /* | 16 | 56 | 0x28 - 0x38 */
int ev_fd; /* 0x38 | 4 | 60 | 0x38 - 0x3c */
short ev_events; /* 0x3c | 2 | 62 | 0x3c - 0x3e */
short ev_res; /* 0x3e | 2 | 64 | 0x3e - 0x40 */
struct event_base * ev_base; /* 0x40 | 8 | 74 | 0x40 - 0x48 */
union { /* 0x48 | ------------ | ---------- | ------------ */
struct { /* | ------------ | | */
LIST_ENTRY (event) ev_io_next; /* | ((16+ | | */
struct timeval ev_timeout; /* | 16)) | | */
} ev_io; /* | ((32)) | | */
struct { /* | ------------ | | */
LIST_ENTRY (event) ev_signal_next; /* | ((16+ | | */
short ev_ncalls; /* | 02+ | | */
short * ev_pncalls; /* | 08)) | | */
} ev_signal; /* | ((26)) | | */
} ev_; /* | 32 | 106 | 0x48 - 0x68 */
struct timeval ev_timeout; /* 0x68 | 16 | 120 | 0x68 - 0x78 */
};
```
We still have a gap here, but the first was removed.
Again, we can save 8 bytes on both 32 and 64 word sizes (32/64 byte cacheline).
Below are the results for testing v2.1.6 -> master -> master + this patch (Release/-O3)
Code:
```C
#include <event2/event.h>
int
main(int argc, char ** argv) {
printf("%zu\n", event_get_struct_event_size());
return 0;
}
```
Branch: `master` (2.2.x)
```
$ gcc -O3 -Wall -Wl,-R/usr/local/lib bleh.c -L/usr/local/lib -o bleh -levent
$ ldd bleh
linux-vdso.so.1 => (0x00007ffc3df50000)
libevent.so.2.2.0 => /usr/local/lib/libevent.so.2.2.0 (0x00007f91fd781000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f91fd3a1000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f91fd182000)
/lib64/ld-linux-x86-64.so.2 (0x00007f91fdbcc000)
$ ./bleh
128
```
Release: `2.1.6`
```
$ gcc -O3 bleh.c -o bleh -levent
$ ldd bleh
linux-vdso.so.1 => (0x00007ffd43773000)
libevent-2.1.so.6 => /usr/lib/x86_64-linux-gnu/libevent-2.1.so.6 (0x00007feb3add6000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007feb3a9f6000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007feb3a7d7000)
/lib64/ld-linux-x86-64.so.2 (0x00007feb3b22a000)
$ ./bleh
128
```
Branch: `this one`
```
$ gcc -O3 -Wl,-R./lib bleh.c -o bleh -L./lib -levent
$ ldd bleh
linux-vdso.so.1 => (0x00007ffff55f7000)
libevent.so.2.2.0 => ./lib/libevent.so.2.2.0 (0x00007ff8e5c82000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ff8e58a2000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007ff8e5683000)
/lib64/ld-linux-x86-64.so.2 (0x00007ff8e60cd000)
$ ./bleh
120
```
183 lines
4.9 KiB
C
183 lines
4.9 KiB
C
/*
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* Copyright (c) 2000-2007 Niels Provos <provos@citi.umich.edu>
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* Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef EVENT2_EVENT_STRUCT_H_INCLUDED_
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#define EVENT2_EVENT_STRUCT_H_INCLUDED_
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/** @file event2/event_struct.h
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Structures used by event.h. Using these structures directly WILL harm
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forward compatibility: be careful.
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No field declared in this file should be used directly in user code. Except
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for historical reasons, these fields would not be exposed at all.
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*/
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <event2/event-config.h>
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#ifdef EVENT__HAVE_SYS_TYPES_H
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#include <sys/types.h>
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#endif
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#ifdef EVENT__HAVE_SYS_TIME_H
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#include <sys/time.h>
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#endif
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/* For int types. */
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#include <event2/util.h>
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/* For evkeyvalq */
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#include <event2/keyvalq_struct.h>
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#define EVLIST_TIMEOUT 0x01
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#define EVLIST_INSERTED 0x02
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#define EVLIST_SIGNAL 0x04
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#define EVLIST_ACTIVE 0x08
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#define EVLIST_INTERNAL 0x10
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#define EVLIST_ACTIVE_LATER 0x20
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#define EVLIST_FINALIZING 0x40
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#define EVLIST_INIT 0x80
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#define EVLIST_ALL 0xff
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/* Fix so that people don't have to run with <sys/queue.h> */
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#ifndef TAILQ_ENTRY
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#define EVENT_DEFINED_TQENTRY_
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#define TAILQ_ENTRY(type) \
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struct { \
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struct type *tqe_next; /* next element */ \
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struct type **tqe_prev; /* address of previous next element */ \
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}
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#endif /* !TAILQ_ENTRY */
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#ifndef TAILQ_HEAD
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#define EVENT_DEFINED_TQHEAD_
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#define TAILQ_HEAD(name, type) \
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struct name { \
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struct type *tqh_first; \
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struct type **tqh_last; \
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}
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#endif
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/* Fix so that people don't have to run with <sys/queue.h> */
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#ifndef LIST_ENTRY
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#define EVENT_DEFINED_LISTENTRY_
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#define LIST_ENTRY(type) \
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struct { \
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struct type *le_next; /* next element */ \
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struct type **le_prev; /* address of previous next element */ \
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}
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#endif /* !LIST_ENTRY */
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#ifndef LIST_HEAD
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#define EVENT_DEFINED_LISTHEAD_
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#define LIST_HEAD(name, type) \
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struct name { \
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struct type *lh_first; /* first element */ \
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}
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#endif /* !LIST_HEAD */
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struct event;
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struct event_callback {
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TAILQ_ENTRY(event_callback) evcb_active_next;
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short evcb_flags;
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ev_uint8_t evcb_pri; /* smaller numbers are higher priority */
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ev_uint8_t evcb_closure;
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/* allows us to adopt for different types of events */
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union {
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void (*evcb_callback)(evutil_socket_t, short, void *);
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void (*evcb_selfcb)(struct event_callback *, void *);
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void (*evcb_evfinalize)(struct event *, void *);
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void (*evcb_cbfinalize)(struct event_callback *, void *);
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} evcb_cb_union;
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void *evcb_arg;
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};
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struct event_base;
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struct event {
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struct event_callback ev_evcallback;
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/* for managing timeouts */
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union {
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TAILQ_ENTRY(event) ev_next_with_common_timeout;
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int min_heap_idx;
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} ev_timeout_pos;
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evutil_socket_t ev_fd;
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short ev_events;
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short ev_res; /* result passed to event callback */
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struct event_base *ev_base;
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union {
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/* used for io events */
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struct {
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LIST_ENTRY (event) ev_io_next;
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struct timeval ev_timeout;
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} ev_io;
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/* used by signal events */
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struct {
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LIST_ENTRY (event) ev_signal_next;
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short ev_ncalls;
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/* Allows deletes in callback */
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short *ev_pncalls;
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} ev_signal;
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} ev_;
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struct timeval ev_timeout;
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};
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TAILQ_HEAD (event_list, event);
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#ifdef EVENT_DEFINED_TQENTRY_
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#undef TAILQ_ENTRY
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#endif
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#ifdef EVENT_DEFINED_TQHEAD_
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#undef TAILQ_HEAD
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#endif
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LIST_HEAD (event_dlist, event);
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#ifdef EVENT_DEFINED_LISTENTRY_
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#undef LIST_ENTRY
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#endif
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#ifdef EVENT_DEFINED_LISTHEAD_
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#undef LIST_HEAD
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#endif
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#ifdef __cplusplus
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}
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#endif
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#endif /* EVENT2_EVENT_STRUCT_H_INCLUDED_ */
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