DAT_SRQ_CREATE(3DAT) Direct Access Transport Library Functions


NAME


dat_srq_create - create an instance of a shared receive queue

SYNOPSIS


cc [ flag... ] file... -ldat [ library... ]
#include <dat/udat.h>

DAT_RETURN
dat_srq_create (
IN DAT_IA_HANDLE ia_handle,
IN DAT_PZ_HANDLE pz_handle,
IN DAT_SRQ_ATTR *srq_attr,
OUT DAT_SRQ_HANDLE *srq_handle
)


PARAMETERS


ia_handle
A handle for an open instance of the IA to which the
created SRQ belongs.


pz_handle
A handle for an instance of the Protection Zone.


srq_attr
A pointer to a structure that contains Consumer-requested
SRQ attributes.


srq_handle
A handle for the created instance of a Shared Receive
Queue.


DESCRIPTION


The dat_srq_create() function creates an instance of a Shared Receive
Queue (SRQ) that is provided to the Consumer as srq_handle. If the value
of DAT_RETURN is not DAT_SUCCESS, the value of srq_handle is not defined.


The created SRQ is unattached to any Endpoints.


The Protection Zone pz_handle allows Consumers to control what local
memory can be used for the Recv DTO buffers posted to the SRQ. Only
memory referred to by LMRs of the posted Recv buffers that match the SRQ
Protection Zone can be accessed by the SRQ.


The srq_attributes argument specifies the initial attributes of the
created SRQ. If the operation is successful, the created SRQ will have
the queue size at least max_recv_dtos and the number of entries on the
posted Recv scatter list of at lease max_recv_iov. The created SRQ can
have the queue size and support number of entries on post Recv buffers
larger than requested. Consumer can query SRQ to find out the actual
supported queue size and maximum Recv IOV.


The Consumer must set low_watermark to DAT_SRQ_LW_DEFAULT to ensure that
an asynchronous event will not be generated immediately, since there are
no buffers in the created SRQ. The Consumer should set the Maximum
Receive DTO attribute and the Maximum number of elements in IOV for
posted buffers as needed.


When an associated EP tries to get a buffer from SRQ and there are no
buffers available, the behavior of the EP is the same as when there are
no buffers on the EP Recv Work Queue.

RETURN VALUES


DAT_SUCCESS
The operation was successful.


DAT_INSUFFICIENT_RESOURCES
The operation failed due to resource
limitations.


DAT_INVALID_HANDLE
Either ia_handle or pz_handle is an invalid
DAT handle.


DAT_INVALID_PARAMETER
One of the parameters is invalid. Either
one of the requested SRQ attributes was
invalid or a combination of attributes is
invalid.


DAT_MODEL_NOT_SUPPORTED
The requested Model was not supported by
the Provider.


USAGE


SRQ is created by the Consumer prior to creation of the EPs that will be
using it. Some Providers might restrict whether multiple EPs that share
a SRQ can have different Protection Zones. Check the
srq_ep_pz_difference_support Provider attribute. The EPs that use SRQ
might or might not use the same recv_evd.


Since a Recv buffer of SRQ can be used by any EP that is using SRQ, the
Consumer should ensure that the posted Recv buffers are large enough to
receive an incoming message on any of the EPs.


If Consumers do not want to receive an asynchronous event when the number
of buffers in SRQ falls below the Low Watermark, they should leave its
value as DAT_SRQ_LW_DEFAULT. If Consumers do want to receive a
notification, they can set the value to the desired one by calling
dat_srq_set_lw(3DAT).


SRQ allows the Consumer to use fewer Recv buffers then posting the
maximum number of buffers for each connection. If the Consumer can upper
bound the number of incoming messages over all connections whose local EP
is using SRQ, then instead of posting this maximum for each connection
the Consumer can post them for all connections on SRQ. For example, the
maximum utilized link bandwidth divided over the message size can be used
for an upper bound.


Depending on the underlying Transport, one or more messages can arrive
simultaneously on an EP that is using SRQ. Thus, the same EP can have
multiple Recv buffers in its possession without these buffers being on
SRQ or recv_evd.


Since Recv buffers can be used by multiple connections of the local EPs
that are using SRQ, the completion order of the Recv buffers is no longer
guaranteed even when they use of the same recv_evd. For each connection
the Recv buffers completion order is guaranteed to be in the order of the
posted matching Sends to the other end of the connection. There is no
ordering guarantee that Receive buffers will be returned in the order
they were posted even if there is only a single connection (Endpoint)
associated with the SRQ. There is no ordering guarantee between
different connections or between different recv_evds.

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+----------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+----------------------+
|Interface Stability | Standard: uDAPL, 1.2 |
+--------------------+----------------------+
|MT-Level | Safe |
+--------------------+----------------------+

SEE ALSO


dat_srq_free(3DAT), dat_srq_post_recv(3DAT), dat_srq_query(3DAT),
dat_srq_resize(3DAT), dat_srq_set_lw(3DAT), libdat(3LIB), attributes(5)


September 11, 2006 DAT_SRQ_CREATE(3DAT)