#include <db.h>
int
DB_ENV->set_thread_id(DB_ENV *dbenv,
    void (*thread_id)(DB_ENV *dbenv, pid_t *pid, db_threadid_t *tid));  
      
         Declare a function that returns a unique identifier pair for the
         current thread of control. The
         DB_ENV->set_thread_id() method supports the
         DB_ENV->failchk()  method.
         For more information, see 
         
             Architecting Data Store and Concurrent Data Store applications
         , and 
         
             Architecting Transactional Data Store applications
         , both in the
         Berkeley DB Programmer's Reference Guide.
    
         The DB_ENV->set_thread_id() method
         configures operations performed using the specified 
         DB_ENV  handle, not all operations
         performed on the underlying database environment.
    
         The DB_ENV->set_thread_id() method may be
         called at any time during the life of the application.
    
         The DB_ENV->set_thread_id() 
            
                  method returns a non-zero error value on failure and 0 on success.
            
            
        
    
The thread_id parameter is a function which returns a unique identifier pair for a thread of control in a Berkeley DB application. The function takes three arguments:
dbenv
The dbenv parameter is the enclosing database environment handle, allowing application access to the application-private fields of that object.
pid
                        The pid points to a memory location of
                        type pid_t, or NULL.  The process ID of the current
                        thread of control may be returned in this memory location, if it is not
                        NULL.
                    
tid
                         The tid points to a memory location of
                         type db_threadid_t, or NULL.  The thread ID of the
                         current thread of control may be returned in this memory location, if it
                         is not NULL.
                     
             The DB_ENV->set_thread_id() 
            
                 method may fail and return one of the following non-zero errors:
            
            
        
        
                The standard system library calls to return process and thread IDs are often sufficient for this
                purpose (for example, getpid() and
                    pthread_self() on POSIX systems or GetCurrentThreadID on Windows
                systems). However, if the Berkeley DB application dynamically creates processes or threads, some
                care may be necessary in assigning unique IDs. In most threading systems, process and thread IDs are
                available for re-use as soon as the process or thread exits. If a new process or thread is created
                between the time of process or thread exit, and the 
                DB_ENV->failchk() method is run, it may be possible for 
                DB_ENV->failchk()                    
                to not detect that a thread of control exited without properly
                releasing all Berkeley DB resources.
        
                It may be possible to handle this problem by inhibiting process or thread
                creation between thread of control exit and calling the 
                DB_ENV->failchk()
                method.  Alternatively, the thread_id function
                must be constructed to not re-use pid/tid
                pairs. For example, in a single process application, the returned process ID
                might be used as an incremental counter, with the returned thread ID set to the
                actual thread ID.  Obviously, the is_alive
                function specified to the 
                DB_ENV->set_isalive() 
                method must be compatible with any
                thread_id function specified to
                DB_ENV->set_thread_id().
        
The db_threadid_t type is configured to be the same type as a standard thread identifier, in Berkeley DB configurations where this type is known (for example, systems supporting pthread_t or thread_t, or DWORD on Windows). If the Berkeley DB configuration process is unable to determine the type of a standard thread identifier, the db_thread_t type is set to uintmax_t (or the largest available unsigned integral type, on systems lacking the uintmax_t type). Applications running on systems lacking a detectable standard thread type, and which are also using thread APIs where a thread identifier is not an integral value and so will not fit into the configured db_threadid_t type, must either translate between the db_threadid_t type and the thread identifier (mapping the thread identifier to a unique identifier of the appropriate size), or modify the Berkeley DB sources to use an appropriate db_threadid_t type. Note: we do not currently know of any systems where this is necessary. If your application has to solve this problem, please contact our support group and let us know.
                If no thread_id function is specified by the
                application, the Berkeley DB library will identify threads of control by using
                the taskIdSelf() call on VxWorks, the
                getpid() and
                GetCurrentThreadID() calls on Windows, the
                getpid() and pthread_self()
                calls when the Berkeley DB library has been configured for POSIX pthreads or
                Solaris LWP threads, the getpid() and
                thr_self() calls when the Berkeley DB library has been
                configured for UI threads, and otherwise getpid().