#include <db.h> int DB_ENV->set_thread_count(DB_ENV *dbenv, u_int32_t count);
Declare an approximate number of threads in the database environment. This method allocates resources in your environment for the threads your application will use. If you fail to properly estimate the number of threads your application will use, your application will run out of resources and errors will be returned when the application attempts to start one too many threads.
The DB_ENV->set_thread_count()
method does not set the
maximum number of threads but is used to determine memory sizing and
the thread control block reclamation policy.
The DB_ENV->set_thread_count()
method must be called
prior to opening the database environment. In addition, this method must be
used with the
DB_ENV->failchk()
method.
If a process invokes this method without the use of DB_ENV->failchk() the program may be unable to allocate a thread control block. This is true of the standalone Berkeley DB utility programs.
If a process has not configured an is_alive function from the
DB_ENV->set_isalive()
method, and then attempts to join a database environment configured
for failure checking with the
DB_ENV->failchk()
,
DB_ENV->set_thread_id()
,
DB_ENV->set_isalive()
and
DB_ENV->set_thread_count()
methods, the program may be unable to
allocate a thread control block and fail to join the environment.
This is true of the standalone Berkeley DB
utility programs. To avoid problems when using the
standalone Berkeley DB utility programs with environments configured
for failure checking, incorporate the utility's functionality directly
in the application, or call the
DB_ENV->failchk()
method
before running the utility.
The database environment's thread count may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "set_thread_count", one or more whitespace characters, and the thread count. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.
The DB_ENV->set_thread_count()
method configures operations performed
using the specified DB_ENV handle, not all
operations performed on the underlying database environment.
The DB_ENV->set_thread_count()
method may not be called after the
DB_ENV->open()
method is
called.
The DB_ENV->set_thread_count()
method returns a non-zero error value on failure and 0 on success.
The DB_ENV->set_thread_count()
method may fail and return one of the following non-zero errors:
If the method was called after DB_ENV->open() was called; or if an invalid flag value or parameter was specified.