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/* Copyright (C) 2008 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
#ifndef _waiting_threads_h
#define _waiting_threads_h
#include <my_global.h>
#include <my_sys.h>
#include <lf.h>
C_MODE_START
typedef struct st_wt_resource_id WT_RESOURCE_ID;
typedef struct st_wt_resource_type {
int (*compare)(void *a, void *b);
const void *(*make_key)(WT_RESOURCE_ID *id, uint *len);
} WT_RESOURCE_TYPE;
/* we want to compare this struct with memcmp, make it packed */
#pragma pack(push,1)
struct st_wt_resource_id {
ulonglong value;
WT_RESOURCE_TYPE *type;
};
#pragma pack(pop)
#define WT_WAIT_STATS 24
#define WT_CYCLE_STATS 32
extern ulonglong wt_wait_table[WT_WAIT_STATS];
extern uint32 wt_wait_stats[WT_WAIT_STATS+1];
extern uint32 wt_cycle_stats[2][WT_CYCLE_STATS+1];
extern uint32 wt_success_stats;
/*
'lock' protects 'owners', 'state', and 'waiter_count'
'id' is read-only
a resource is picked up from a hash in a lock-free manner
it's returned pinned, so it cannot be freed at once
but it may be freed right after the pin is removed
to free a resource it should be
1. have no owners
2. have no waiters
two ways to access a resource:
1. find it in a hash
- it's returned pinned.
a) take a lock in exclusive mode
b) check the state, it should be ACTIVE
c) unpin
2. by a direct reference
- could only used if a resource cannot be freed
e.g. accessing a resource by thd->waiting_for is safe,
a resource cannot be freed as there's a thread waiting for it
*/
typedef struct st_wt_resource {
WT_RESOURCE_ID id;
uint waiter_count;
enum { ACTIVE, FREE } state;
#ifndef DBUG_OFF
pthread_mutex_t *mutex;
#endif
/*
before the 'lock' all elements are mutable, after (and including) -
immutable in the sense that lf_hash_insert() won't memcpy() over them.
See wt_init().
*/
#ifdef WT_RWLOCKS_USE_MUTEXES
/*
we need a special rwlock-like 'lock' to allow readers bypass
waiting writers, otherwise readers can deadlock.
writer starvation is technically possible, but unlikely, because
the contention is expected to be low.
*/
struct {
pthread_cond_t cond;
pthread_mutex_t mutex;
uint readers: 16;
uint pending_writers: 15;
uint write_locked: 1;
} lock;
#else
rw_lock_t lock;
#endif
pthread_cond_t cond;
DYNAMIC_ARRAY owners;
} WT_RESOURCE;
typedef struct st_wt_thd {
/*
XXX
there's no protection (mutex) against concurrent access of
the dynarray below. it is assumed that a caller will have it
automatically (not to protect this array but to protect its
own - caller's - data structures, and we'll get it for free.
If not, we'll need to add a mutex
*/
DYNAMIC_ARRAY my_resources;
/*
'waiting_for' is modified under waiting_for->lock, and only by thd itself
'waiting_for' is read lock-free (using pinning protocol), but a thd object
can read its own 'waiting_for' without any locks or tricks.
*/
WT_RESOURCE *waiting_for;
LF_PINS *pins;
/* pointers to values */
ulong *timeout_short, *deadlock_search_depth_short;
ulong *timeout_long, *deadlock_search_depth_long;
/*
weight relates to the desirability of a transaction being killed if it's
part of a deadlock. In a deadlock situation transactions with lower weights
are killed first.
Examples of using the weight to implement different selection strategies:
1. Latest
Keep all weights equal.
2. Random
Assight weights at random.
(variant: modify a weight randomly before every lock request)
3. Youngest
Set weight to -NOW()
4. Minimum locks
count locks granted in your lock manager, store the value as a weight
5. Minimum work
depends on the definition of "work". For example, store the number
of rows modifies in this transaction (or a length of REDO log for a
transaction) as a weight.
It is only statistically relevant and is not protected by any locks.
*/
ulong volatile weight;
/*
'killed' is indirectly protected by waiting_for->lock -
a killed thread needs to clear its 'waiting_for', and thus needs a lock.
That is a thread needs an exclusive lock to read 'killed' reliably.
But other threads may change 'killed' from 0 to 1, a shared
lock is enough for that.
*/
my_bool volatile killed;
#ifndef DBUG_OFF
const char *name;
#endif
} WT_THD;
#define WT_TIMEOUT ETIMEDOUT
#define WT_OK 0
#define WT_DEADLOCK -1
#define WT_DEPTH_EXCEEDED -2
void wt_init(void);
void wt_end(void);
void wt_thd_lazy_init(WT_THD *, ulong *, ulong *, ulong *, ulong *);
void wt_thd_destroy(WT_THD *);
int wt_thd_will_wait_for(WT_THD *, WT_THD *, WT_RESOURCE_ID *);
int wt_thd_cond_timedwait(WT_THD *, pthread_mutex_t *);
void wt_thd_release(WT_THD *, WT_RESOURCE_ID *);
#define wt_thd_release_all(THD) wt_thd_release((THD), 0)
int wt_resource_id_memcmp(void *, void *);
C_MODE_END
#endif