BDB事务共享区域

/*
* The transaction manager encapsulates the transaction system. It contains
* references to the log and lock managers as well as the state that keeps
* track of the shared memory region.
*/
struct __db_txnmgr {
/* These fields need to be protected for multi-threaded support. */
 db_mutex_t *mutexp; /* Synchronization. */
 /* list of active transactions */
 TAILQ_HEAD(_chain, __db_txn) txn_chain;
/* These fields are not protected. */
 REGINFO reginfo; /* Region information. */
 DB_ENV *dbenv; /* Environment. */
 int (*recover) /* Recovery dispatch routine */
 __P((DB_LOG *, DBT *, DB_LSN *, int, void *));
 u_int32_t flags; /* DB_TXN_NOSYNC, DB_THREAD */
 DB_TXNREGION *region; /* address of shared memory region */
 void *mem; /* address of the shalloc space */
};

/*
* Layout of the shared memory region.
* The region consists of a DB_TXNREGION structure followed by a large
* pool of shalloc'd memory which is used to hold TXN_DETAIL structures
* and thread mutexes (which are dynamically allocated).
*/
struct __db_txnregion {
 RLAYOUT hdr; /* Shared memory region header. */
 u_int32_t magic; /* transaction magic number */
 u_int32_t version; /* version number */
 u_int32_t maxtxns; /* maximum number of active txns */
 u_int32_t last_txnid; /* last transaction id given out */
 DB_LSN pending_ckp; /* last checkpoint did not finish */
 DB_LSN last_ckp; /* lsn of the last checkpoint */
 time_t time_ckp; /* time of last checkpoint */
 u_int32_t logtype; /* type of logging */
 u_int32_t locktype; /* lock type */
 u_int32_t naborts; /* number of aborted transactions */
 u_int32_t ncommits; /* number of committed transactions */
 u_int32_t nbegins; /* number of begun transactions */
 SH_TAILQ_HEAD(_active) active_txn; /* active transaction list */
};

if (LF_ISSET(DB_INIT_TXN) && (ret = txn_open(NULL,
 LF_ISSET(DB_CREATE | DB_THREAD | DB_TXN_NOSYNC),
 mode, dbenv, &dbenv->tx_info)) != 0)
 goto err;

int
txn_open(path, flags, mode, dbenv, mgrpp)
 const char *path;
 u_int32_t flags;
 int mode;
 DB_ENV *dbenv;
 DB_TXNMGR **mgrpp;
{
 DB_TXNMGR *tmgrp;
 u_int32_t maxtxns;
 int ret;
 /* Validate arguments. */
 首先仍然是验证参数
 然后用malloc创建每个进程都有的事务管理器结构
 /* Now, create the transaction manager structure and set its fields. */
 if ((ret = __os_calloc(1, sizeof(DB_TXNMGR), &tmgrp)) != 0)
 return (ret);
 并初始化事务管理器结构
 /* Initialize the transaction manager structure. */
 tmgrp->mutexp = NULL;
 tmgrp->dbenv = dbenv;
 tmgrp->recover =
 dbenv->tx_recover == NULL ? __db_dispatch : dbenv->tx_recover;
 tmgrp->flags = LF_ISSET(DB_TXN_NOSYNC | DB_THREAD);
 TAILQ_INIT(&tmgrp->txn_chain);
 现在开始创建或连接到一个事务共享区域
 /* Join/create the txn region. */
 首先还是一样，填充区域描述信息REGINFO{}，然后调用__db_rattach()函数创建或打开一个共享区域
 tmgrp->reginfo.dbenv = dbenv;
 tmgrp->reginfo.appname = DB_APP_NONE;
 if (path == NULL)
 tmgrp->reginfo.path = NULL;
 else
 if ((ret = __os_strdup(path, &tmgrp->reginfo.path)) != 0)
 goto err;
 tmgrp->reginfo.file = DEFAULT_TXN_FILE;
 tmgrp->reginfo.mode = mode;
 tmgrp->reginfo.size = TXN_REGION_SIZE(maxtxns);
 tmgrp->reginfo.dbflags = flags;
 tmgrp->reginfo.addr = NULL;
 tmgrp->reginfo.fd = -1;
 tmgrp->reginfo.flags = dbenv->tx_max == 0 ? REGION_SIZEDEF : 0;
 if ((ret = __db_rattach(&tmgrp->reginfo)) != 0)
 goto err;
 /* Fill in region-related fields. */
 tmgrp->region = tmgrp->reginfo.addr;
 tmgrp->mem = &tmgrp->region[1];
 if (F_ISSET(&tmgrp->reginfo, REGION_CREATED)) {
 tmgrp->region->maxtxns = maxtxns;
 if ((ret = __txn_init(tmgrp->region)) != 0)
 goto err;
 } else if (tmgrp->region->magic != DB_TXNMAGIC) {
 /* Check if valid region. */
 __db_err(dbenv, "txn_open: Bad magic number");
 ret = EINVAL;
 goto err;
 }
 // 如果这是一个新的事务共享区域，初始化之。这里又和MPOOL一样，
 // 使用__shmalloc函数管理共享区域内存
 if (LF_ISSET(DB_THREAD)) {
 if ((ret = __db_shalloc(tmgrp->mem, sizeof(db_mutex_t),
 MUTEX_ALIGNMENT, &tmgrp->mutexp)) == 0)
 /*
 * Since we only get here if threading is turned on, we
 * know that we have spinlocks, so the offset is going
 * to be ignored. We put 0 here as a valid placeholder.
 */
 __db_mutex_init(tmgrp->mutexp, 0);
 if (ret != 0)
 goto err;
 }
 UNLOCK_TXNREGION(tmgrp);
 *mgrpp = tmgrp;
 return (0);
err: if (tmgrp->reginfo.addr != NULL) {
 if (tmgrp->mutexp != NULL)
 __db_shalloc_free(tmgrp->mem, tmgrp->mutexp);
 UNLOCK_TXNREGION(tmgrp);
 (void)__db_rdetach(&tmgrp->reginfo);
 if (F_ISSET(&tmgrp->reginfo, REGION_CREATED))
 (void)txn_unlink(path, 1, dbenv);
 }
 if (tmgrp->reginfo.path != NULL)
 __os_freestr(tmgrp->reginfo.path);
 __os_free(tmgrp, sizeof(*tmgrp));
 return (ret);
}

/*
* This file contains the top level routines of the transaction library.
* It assumes that a lock manager and log manager that conform to the db_log(3)
* and db_lock(3) interfaces exist.
*
* Initialize a transaction region in shared memory.
* Return 0 on success, errno on failure.
*/
static int
__txn_init(txn_region)
 DB_TXNREGION *txn_region;
{
 time_t now;
 (void)time(&now);
 /* maxtxns is already initialized. */
 txn_region->magic = DB_TXNMAGIC;
 txn_region->version = DB_TXNVERSION;
 txn_region->last_txnid = TXN_MINIMUM;
 /*
 * XXX
 * If we ever do more types of locking and logging, this changes.
 */
 txn_region->logtype = 0;
 txn_region->locktype = 0;
 txn_region->time_ckp = now;
 ZERO_LSN(txn_region->last_ckp);
 ZERO_LSN(txn_region->pending_ckp);
 SH_TAILQ_INIT(&txn_region->active_txn);
 __db_shalloc_init((void *)&txn_region[1],
 TXN_REGION_SIZE(txn_region->maxtxns) - sizeof(DB_TXNREGION));
 return (0);
}

/* The structure allocated for every transaction. */
struct __db_txn {
 DB_TXNMGR *mgrp; /* Pointer to transaction manager. */
 DB_TXN *parent; /* Pointer to transaction's parent. */
 DB_LSN last_lsn; /* Lsn of last log write. */
 u_int32_t txnid; /* Unique transaction id. */
 size_t off; /* Detail structure within region. */
 TAILQ_ENTRY(__db_txn) links; /* Links transactions off manager. */
 TAILQ_HEAD(__kids, __db_txn) kids; /* Child transactions. */
 TAILQ_ENTRY(__db_txn) klinks; /* Links child transactions. */
#define TXN_MALLOC 0x01 /* Structure allocated by TXN system. */
 u_int32_t flags;
};
typedef struct __txn_detail {
 u_int32_t txnid; /* current transaction id
 used to link free list also */
 DB_LSN last_lsn; /* last lsn written for this txn */
 DB_LSN begin_lsn; /* lsn of begin record */
 size_t last_lock; /* offset in lock region of last lock
 for this transaction. */
 size_t parent; /* Offset of transaction's parent. */
#define TXN_UNALLOC 0
#define TXN_RUNNING 1
#define TXN_ABORTED 2
#define TXN_PREPARED 3
#define TXN_COMMITTED 4
 u_int32_t status; /* status of the transaction */
 SH_TAILQ_ENTRY links; /* free/active list */
#define TXN_XA_ABORTED 1
#define TXN_XA_DEADLOCKED 2
#define TXN_XA_ENDED 3
#define TXN_XA_PREPARED 4
#define TXN_XA_STARTED 5
#define TXN_XA_SUSPENDED 6
 u_int32_t xa_status; /* XA status */
 /*
 * XID (xid_t) structure: because these fields are logged, the
 * sizes have to be explicit.
 */
 DB_XID xid; /* XA global transaction id */
 u_int32_t bqual; /* bqual_length from XID */
 u_int32_t gtrid; /* gtrid_length from XID */
 int32_t format; /* XA format */
} TXN_DETAIL;