Berkeley DB: DbLockTab::unlink
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btr ee,hash,hashing,transaction,transactions,locking,logging,access method,access me thods,java,C,C++

# DbLockTab::unlink

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    #include <db_cxx.h>

    static int
    DbLockTab::unlink(const char *dir, int force, DbEnv *dbenv);

# Description

The DbLockTab::unlink function destroys the lock table identified by the directory dir, removing all files used to implement the lock table. (The directory dir is not removed.)

If there are processes that have called DbLockTab::open without calling DbLockTab::close (i.e., there are processes currently using the lock table), DbLockTab::unlink will fail without further action, unless the force flag is set, in which case DbLockTab::unlink will attempt to remove the lock table files regardless of any processes still using it.

The result of attempting to forcibly destroy the region when a process has the region open is unspecified. Processes using a shared memory region maintain an open file descriptor for it. On UNIX systems, the region removal should succeed and processes that have already joined the region should continue to run in the region without change, however processes attempting to join the lock table will either fail or attempt to create a new region. On other systems (e.g., Windows/NT), where the unlink(2) system call will fail if any process has an open file descriptor for the file, the region removal will fail.

In the case of catastrophic or system failure, database recovery must be performed (see db_recover), or the DB_RECOVER and DB_RECOVER_FATAL flags to DbEnv::appinit must be specified. Alternatively, if recovery is not required because no database state is maintained across failures, it is possible to clean up a lock table by removing all of the files in the directory specified to the DbLockTab::open function, as no lock table files are created in any other directory. Note, however, that this has the potential to remove files created by the other Berkeley DB subsystems in the same database environment.

The DbLockTab::unlink method either returns errno or throws an exception that encapsulates an errno on failure, and 0 on success.

# Errors

If a fatal error occurs in Berkeley DB, the DbLockTab::unlink method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, at which point all subsequent database calls will also fail in the same way. Methods marked as returning errno will, by default, throw an exception that encapsulates the error information. The default error behavior can be changed, see DbException.

The DbLockTab::unlink method may fail and throw an exception for any of the errors specified for the following Berkeley DB and C library functions: abort(3), close(3), DbEnv::version, fcntl(3), fflush(3), fprintf(3), free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3), 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 DbLockTab::unlink method may fail and throw an exception or return errno for the following conditions:

EBUSY
  The shared memory region was in use and the force flag was not set.

# Class

DbLockTab

# See Also

DbLockTab::close, DbLockTab::detect, DbLockTab::get, DbLockTab::id, DbLockTab::open, DbLockTab::stat DbLockTab::unlink and DbLockTab::vec.`