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/*-
* Copyright (c) 2014-2016 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
/*
* Condition variables:
*
* WiredTiger uses condition variables to signal between threads, and for
* locking operations that are expected to block.
*/
struct __wt_condvar {
const char *name; /* Mutex name for debugging */
wt_mutex_t mtx; /* Mutex */
wt_cond_t cond; /* Condition variable */
int waiters; /* Numbers of waiters, or
-1 if signalled with no waiters. */
/*
* The following fields are only used for automatically adjusting
* condition variables. They could be in a separate structure.
*/
uint64_t min_wait; /* Minimum wait duration */
uint64_t max_wait; /* Maximum wait duration */
uint64_t prev_wait; /* Wait duration used last time */
};
/*
* !!!
* Don't modify this structure without understanding the read/write locking
* functions.
*/
typedef union { /* Read/write lock */
uint64_t u;
struct {
uint32_t wr; /* Writers and readers */
} i;
struct {
uint16_t writers; /* Now serving for writers */
uint16_t readers; /* Now serving for readers */
uint16_t users; /* Next available ticket number */
uint16_t __notused; /* Padding */
} s;
} wt_rwlock_t;
/*
* Read/write locks:
*
* WiredTiger uses read/write locks for shared/exclusive access to resources.
*/
struct __wt_rwlock {
const char *name; /* Lock name for debugging */
wt_rwlock_t rwlock; /* Read/write lock */
};
/*
* A light weight lock that can be used to replace spinlocks if fairness is
* necessary. Implements a ticket-based back off spin lock.
* The fields are available as a union to allow for atomically setting
* the state of the entire lock.
*/
struct __wt_fair_lock {
union {
uint32_t lock;
struct {
uint16_t owner; /* Ticket for current owner */
uint16_t waiter; /* Last allocated ticket */
} s;
} u;
#define fair_lock_owner u.s.owner
#define fair_lock_waiter u.s.waiter
};
/*
* Spin locks:
*
* WiredTiger uses spinlocks for fast mutual exclusion (where operations done
* while holding the spin lock are expected to complete in a small number of
* instructions).
*/
#define SPINLOCK_GCC 0
#define SPINLOCK_MSVC 1
#define SPINLOCK_PTHREAD_MUTEX 2
#define SPINLOCK_PTHREAD_MUTEX_ADAPTIVE 3
#if SPINLOCK_TYPE == SPINLOCK_GCC
struct WT_COMPILER_TYPE_ALIGN(WT_CACHE_LINE_ALIGNMENT) __wt_spinlock {
volatile int lock;
};
#elif SPINLOCK_TYPE == SPINLOCK_PTHREAD_MUTEX ||\
SPINLOCK_TYPE == SPINLOCK_PTHREAD_MUTEX_ADAPTIVE ||\
SPINLOCK_TYPE == SPINLOCK_MSVC
struct WT_COMPILER_TYPE_ALIGN(WT_CACHE_LINE_ALIGNMENT) __wt_spinlock {
wt_mutex_t lock;
const char *name; /* Statistics: mutex name */
int8_t initialized; /* Lock initialized, for cleanup */
};
#else
#error Unknown spinlock type
#endif
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