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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH DAT_EVD_DEQUEUE 3DAT "Jul 16, 2004" .SH NAME dat_evd_dequeue \- remove the first event from the Event Dispatcher event queue .SH SYNOPSIS .LP .nf cc [ \fIflag\fR\&.\|.\|. ] \fIfile\fR\&.\|.\|. \fB-ldat\fR [ \fIlibrary\fR\&.\|.\|. ] #include <\fBdat/udat.h\fR> DAT_RETURN dat_evd_dequeue( IN DAT_EVD_HANDLE \fIevd_handle\fR, OUT DAT_EVENT *\fIevent\fR ) .fi .SH PARAMETERS .sp .ne 2 .na \fB\fIevd_handle\fR\fR .ad .RS 14n Handle for an instance of the Event Dispatcher. .RE .sp .ne 2 .na \fB\fIevent\fR\fR .ad .RS 14n Pointer to the Consumer-allocated structure that Provider fills with the event data. .RE .SH DESCRIPTION .sp .LP The \fBdat_evd_dequeue()\fR function removes the first event from the Event Dispatcher event queue and fills the Consumer allocated \fIevent\fR structure with event data. The first element in this structure provides the type of the event; the rest provides the event-type-specific parameters. The Consumer should allocate an \fIevent\fR structure big enough to hold any event that the Event Dispatcher can deliver. .sp .LP For all events the Provider fills the \fBdat_event\fR that the Consumer allocates. So for all events, all fields of \fBdat_event\fR are OUT from the Consumer point of view. For \fBDAT_CONNECTION_REQUEST_EVENT\fR, the Provider creates a Connection Request whose \fIcr_handle\fR is returned to the Consumer in \fBDAT_CR_ARRIVAL_EVENT_DATA\fR. That object is destroyed by the Provider as part of \fBdat_cr_accept\fR(3DAT), \fBdat_cr_reject\fR(3DAT), or \fBdat_cr_handoff\fR(3DAT). The Consumer should not use \fIcr_handle\fR or any of its parameters, including \fIprivate_data\fR, after one of these operations destroys the Connection Request. .sp .LP For \fBDAT_CONNECTION_EVENT_ESTABLISHED\fR for the Active side of connection establishment, the Provider returns the pointer for \fIprivate_data\fR and the \fIprivate_data_size\fR. For the Passive side, \fBDAT_CONNECTION_EVENT_ESTABLISHED\fR event \fIprivate_data\fR is not defined and \fIprivate_data_size\fR returns zero. The Provider is responsible for the memory allocation and deallocation for \fIprivate_data\fR. The \fIprivate_data\fR is valid until the Active side Consumer destroys the connected Endpoint (\fBdat_ep_free\fR(3DAT)), or transitions the Endpoint into Unconnected state so it is ready for the next connection. So while the Endpoint is in Connected, Disconnect Pending, or Disconnected state, the private_data of \fBDAT_CONNECTION_REQUEST_EVENT\fR is still valid for Active side Consumers. .sp .LP Provider must pass to the Consumer the entire Private Data that the remote Consumer provided for \fBdat_ep_connect\fR(3DAT), \fBdat_ep_dup_connect\fR(3DAT), and \fBdat_cr_accept()\fR. If the Consumer provides more data than the Provider and Transport can support (larger than IA Attribute of \fImax_private_data_size\fR), \fBDAT_INVALID_PARAMETER\fR is returned for that operation. .sp .LP The returned event that was posted from an Event Stream guarantees Consumers that all events that were posted from the same Event Stream prior to the returned event were already returned to a Consumer directly through a \fBdat_evd_dequeue()\fR or \fBdat_evd_wait\fR(3DAT) operation. .sp .LP The ordering of events dequeued by overlapping calls to \fBdat_evd_wait()\fR or \fBdat_evd_dequeue()\fR is not specified. .SH RETURN VALUES .sp .ne 2 .na \fB\fBDAT_SUCCESS\fR\fR .ad .RS 22n The operation was successful. An event was returned to a Consumer. .RE .sp .ne 2 .na \fB\fBDAT_INVALID_HANDLE\fR\fR .ad .RS 22n Invalid DAT handle; evd_handle is invalid. .RE .sp .ne 2 .na \fB\fBDAT_QUEUE_EMPTY\fR\fR .ad .RS 22n There are no entries on the Event Dispatcher queue. .RE .sp .ne 2 .na \fB\fBDAT_INVALID_STATE\fR\fR .ad .RS 22n One of the parameters was invalid for this operation. There is already a waiter on the EVD. .RE .SH USAGE .sp .LP No matter how many contexts attempt to dequeue from an Event Dispatcher, each event is delivered exactly once. However, which Consumer receives which event is not defined. The Provider is not obligated to provide the first caller the first event unless it is the only caller. The Provider is not obligated to ensure that the caller receiving the first event executes earlier than contexts receiving later events. .sp .LP Preservation of event ordering within an Event Stream is an important feature of the DAT Event Model. Consumers are cautioned that overlapping or concurrent calls to \fBdat_evd_dequeue()\fR from multiple contexts can undermine this ordering information. After multiple contexts are involved, the Provider can only guarantee the order that it delivers events into the EVD. The Provider cannot guarantee that they are processed in the correct order. .sp .LP Although calling \fBdat_evd_dequeue()\fR does not cause a context switch, the Provider is under no obligation to prevent one. A context could successfully complete a dequeue, and then reach the end of its timeslice, before returning control to the Consumer code. Meanwhile, a context receiving a later event could be executing. .sp .LP The Event ordering is preserved when dequeueing is serialized. Potential Consumer serialization methods include, but are not limited to, performing all dequeueing from a single context or protecting dequeueing by way of lock or semaphore. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(7) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Standard: uDAPL, 1.1, 1.2 _ MT-Level Safe .TE .SH SEE ALSO .sp .LP .BR dat_cr_accept (3DAT), .BR dat_cr_handoff (3DAT), .BR dat_cr_reject (3DAT), .BR dat_ep_connect (3DAT), .BR dat_ep_dup_connect (3DAT), .BR dat_ep_free (3DAT), .BR dat_evd_wait (3DAT), .BR libdat (3LIB), .BR attributes (7)