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Normally, the doors library creates new door server threads in response to incoming concurrent door invocations automatically. There is no pre-defined upper limit on the number of server threads that the system creates in response to incoming invocations
(1 server thread for each active door invocation). These threads are created with the default thread stack size and POSIX (see standards(5)) threads cancellation
disabled. The created threads also have the THR_BOUND | THR_DETACHED attributes for Solaris threads and the PTHREAD_SCOPE_SYSTEM | PTHREAD_CREATE_DETACHED attributes for POSIX threads. The signal disposition, and scheduling class of the newly created thread are inherited from the calling thread (initially from the thread calling door_create(), and subsequently from the current active door server thread).
The door_server_create() function allows control over the creation of server threads needed for door invocations. The procedure create_proc is called every time the available server thread pool is depleted. In the case of private server pools associated
with a door (see the DOOR_PRIVATE attribute in door_create()), information on which pool is depleted is passed to the create function in the form of a door_info_t structure. The di_proc and di_data members of the door_info_t structure can be used as a door identifier associated with the depleted pool. The create_proc procedure may limit the number of server threads created and may also create server threads with appropriate attributes
(stack size, thread-specific data, POSIX thread cancellation, signal mask, scheduling attributes, and so forth) for use with door invocations.
The specified server creation function should create user level threads using thr_create() with the THR_BOUND flag, or in the case of POSIX threads, pthread_create() with the PTHREAD_SCOPE_SYSTEM attribute. The server threads make themselves available for incoming door invocations on this process by issuing a door_return(NULL, 0, NULL, 0). In this case, the door_return() arguments are ignored. See door_return(3DOOR) and thr_create(3THR).
The server threads created by default are enabled for POSIX thread cancellations which may lead to unexpected thread terminations while holding resources (such as locks) if the client aborts the associated door_call(). See door_call(3DOOR). Unless the server code is truly interested in notifications of client aborts during a door invocation and is prepared to handle such notifications using cancellation handlers, POSIX thread cancellation should be disabled
for server threads using pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, NULL).
The create_proc procedure need not create any additional server threads if there is at least one server thread currently active in the process (perhaps handling another door invocation) or it may create as many as seen fit each time it is called. If there are no available
server threads during an incoming door invocation, the associated door_call() blocks until a server thread becomes available. The create_proc procedure must be MT-Safe.
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