+I%Berkeley DB: lock_open[P

lock_open





#include <db.h>

int+lock_open(const char *dir, u_int32_t flags,3 int mode, DB_ENV *dbenv, DB_LOCKTAB **regionp);





Description

The lock_openRfunction copies a pointer, to the "lock region" identified by the directoryBdir, into the memory location referenced by regionp.

The;dir pathname argument is interpreted as described in@Berkeley DB File Naming.

KThe flags and mode arguments specify how files will be opened,and/or created if they do not already exist.SThe flags value is specified by logically OR'ing together one or more of thefollowing values:

[

DB_CREATE
Create any underlying files, as necessary. If the files do not alreadyBexist and the DB_CREATE flag is not specified, the call will fail.[

DB_THREAD
Cause the m4_reg(DB_LOCKTAB) handle returned by lock_open to be useable>by multiple threads within a single address space, i.e., to befree-threaded.


WAll files created by the lock subsystem are created with mode mode (as describedHin chmod(2)) and modified by the process' umask value at the time$of creation (see umask(2)))).IThe group ownership of created files is based on the system and directory6defaults, and is not further specified by Berkeley DB.

#The locking subsystem is configuredEbased on the dbenv argument to lock_open which is a pointer toFa structure of type DB_ENV. Applications normally use the same DB_ENVkstructure (initialized by db_appinit) as an argument to all of*the subsystems in the Berkeley DB package.

OReferences to the DB_ENV structure are maintained by Berkeley DB, so it may notDbe discarded until the last close function, corresponding to an open?function for which it was an argument, has returned. To ensureKcompatibility with future releases of Berkeley DB, all fields of the DB_ENVGstructure that are not explicitly set should be initialized to 0 beforeIthe first time the structure is used. Do this by declaring the structure?external or static, or by calling one of the C library routines$bzero(3) or memset(3).

IThe fields of the DB_ENV structure used by lock_open are described below.CIf dbenv is NULL or any of its fields are set to 0, defaults3appropriate for the system are used where possible.

FThe following fields in the DB_ENV structure may be initialized beforecalling lock_open:

>

void *(*db_errcall)(char *db_errpfx, char *buffer);

FILE *db_errfile;

const char *db_errpfx;
int db_verbose;
The error fields of the DB_ENV behave as described for db_appinit.V

const u_int8_t lk_conflicts[][];
A lk_modes by lk_modes array.$A non-0 value for the array element:A

    lk_conflicts[requested_mode][held_mode]

5indicates that requested_mode and held_mode conflict.5The not-granted mode must be represented by 0.3If lk_conflicts is NULL, the conflicts array‚db_rw_conflicts is used; see Standard Lock Modes for a description of that array.f

db_detect_t lk_detect;
If non-0, specifies that the deadlock detector be run whenever a lockEconflict occurs, and specifies which transaction should be aborted inthe case of a deadlock.FThe lk_detect field must be set to one of the following values.
z

DB_LOCK_DEFAULT
Use the default policy as specified by db_deadlock.6

DB_LOCK_OLDEST
Abort the oldest transaction.M

DB_LOCK_RANDOM
Abort a random transaction involved in the deadlock.:

DB_LOCK_YOUNGEST
Abort the youngest transaction.
]

u_int32_t lk_max;
The maximum number of locks to be held or requested in the table.=This value is used by lock_open to estimate how much space to0allocate for various lock-table data structures./If lk_max is 0, a default value is used.d

u_int32_t lk_modes;
The number of lock modes to be recognized by the lock table (includingAthe not-granted mode). If lk_modes is 0, the value?DB_LOCK_RW_N is used.


The lock_openHfunction returns the value of errno on failure, and 0 on success.



Environment Variables

Q

DB_HOME
If the dbenv argument to lock_open was initialized usingcdb_appinit the environment variable DB_HOME mayBbe used as the path of the database home for the interpretation ofthe dir argument.


V

TMPDIR
If the dbenv argument to lock_open was NULL or not initializedhusing db_appinit the environment variable TMPDIR mayKbe used as the directory in which to create the lock table, as described in lock_open.




Errors

RIf a fatal error occurs in Berkeley DB, the lock_open function may fail and returnFDB_RUNRECOVERY, at which point all subsequent database calls will alsoreturn DB_RUNRECOVERY.

The lock_open)function may fail and return errnoKfor any of the errors specified for the following Berkeley DB and C library functions: abort(3), close(3),8db_version, fcntl(3), fflush(3), fprintf(3),free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3),<lock_unlink, lseek(3), malloc(3), memcpy(3), memset(3),mmap(3), munmap(3),open(3),pstat_getdynamic(3),read(3), shmat(3), shmctl(3), shmdt(3),sigfillset(3),sigprocmask(3),stat(3), strerror(3), strlen(3), sysconf(3), unlink(3), vfprintf(3), vsnprintf(3),and write(3).

In addition, the lock_open)function may fail and return errnofor the following conditions:

R

EAGAIN
The shared memory region was locked and (repeatedly) unavailable.
B

EINVAL
An invalid flag value or parameter was specified.

FThe DB_THREAD flag was specified and spinlocks are not implemented forthis architecture.





See Also

:lock_close,<lock_detect,6lock_get,4lock_id, lock_open,3lock_put,8lock_stat,;lock_unlinkand6lock_vec.
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