LIBRARYOpenLDAP LDAP (libldap, -lldap)
ldap_dup() duplicates an existing LDAP (LDAP *) session handle. The new session handle may be used concurrently with the original session handle. In a threaded environment, different threads may execute concurrent requests on the same connection/session without fear of contamination. Each session handle manages its own private error results.
ldap_destroy() destroys an existing session handle.
The ldap_dup() and ldap_destroy() functions are used in conjunction with a "thread safe" version of libldap (libldap_r) to enable operation thread safe API calls, so that a single session may be simultaneously used across multiple threads with consistent error handling.
When a session is created through the use of one of the session creation functions including ldap_open(3), ldap_init(3), ldap_initialize(3) or ldap_init_fd(3) an LDAP * session handle is returned to the application. The session handle may be shared amongst threads, however the error codes are unique to a session handle. Multiple threads performing different operations using the same session handle will result in inconsistent error codes and return values.
To prevent this confusion, ldap_dup() is used duplicate an existing session handle so that multiple threads can share the session, and maintain consistent error information and results.
The message queues for a session are shared between sibling session handles. Results of operations on a sibling session handles are accessible to all the sibling session handles. Applications desiring results associated with a specific operation should provide the appropriate msgid to ldap_result(). Applications should avoid calling ldap_result() with LDAP_RES_ANY as that may "steal" and return results in the calling thread that another operation in a different thread, using a different session handle, may require to complete.
When ldap_unbind() is called on a session handle with siblings, all the siblings become invalid.
Siblings must be destroyed using ldap_destroy(). Session handle resources associated with the original (LDAP *) will be freed when the last session handle is destroyed or when ldap_unbind() is called, if no other session handles currently exist.
ERRORSIf an error occurs, ldap_dup() will return NULL and errno should be set appropriately. ldap_destroy() will directly return the LDAP code associated to the error (or LDAP_SUCCESS in case of success); errno should be set as well whenever appropriate.
ACKNOWLEDGEMENTSThis work is based on the previously proposed LDAP C API Concurrency Extensions draft (draft-zeilenga-ldap-c-api-concurrency-00.txt) effort. OpenLDAP Software is developed and maintained by The OpenLDAP Project <http://www.openldap.org/>. OpenLDAP Software is derived from University of Michigan LDAP 3.3 Release.