DAT_SRQ_POST_RECV(3DAT) Direct Access Transport Library Functions


dat_srq_post_recv - add receive buffers to shared receive queue


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

dat_srq_post_recv (
IN DAT_SRQ_HANDLE srq_handle,
IN DAT_COUNT num_segments,
IN DAT_LMR_TRIPLET *local_iov,
IN DAT_DTO_COOKIE user_cookie


A handle for an instance of the SRQ.

The number of lmr_triplets in local_iov. Can be 0 for
receiving a zero-size message.

An I/O Vector that specifies the local buffer to be
filled. Can be NULL for receiving a zero-size message.

A user-provided cookie that is returned to the Consumer
at the completion of the Receive DTO. Can be NULL.


The dat_srq_post_recv() function posts the receive buffer that can be
used for the incoming message into the local_iov by any connected EP that
uses SRQ.

The num_segments argument specifies the number of segments in the
local_iov. The local_iov segments are filled in the I/O Vector order
until the whole message is received. This ensures that all the front
segments of the local_iov I/O Vector are completely filled, only one
segment is partially filled, if needed, and all segments that follow it
are not filled at all. The actual order of segment fillings is left to
the implementation.

The user_cookie argument allows Consumers to have unique identifiers for
each DTO. These identifiers are completely under user control and are
opaque to the Provider. There is no requirement on the Consumer that the
value user_cookie should be unique for each DTO. The user_cookie is
returned to the Consumer in the Completion event for the posted Receive.

The completion of the posted Receive is reported to the Consumer
asynchronously through a DTO Completion event based on the configuration
of the EP that dequeues the posted buffer and the specified
completion_flags value for Solicited Wait for the matching Send. If EP
Recv Completion Flag is DAT_COMPLETION_UNSIGNALLED_FLAG, which is the
default value for SRQ EP, then all posted Recvs will generate completions
with Signal Notifications.

A Consumer should not modify the local_iov or its content until the DTO
is completed. When a Consumer does not adhere to this rule, the behavior
of the Provider and the underlying Transport is not defined. Providers
that allow Consumers to get ownership of the local_iov but not the memory
it specified back after the dat_srq_post_recv() returns should document
this behavior and also specify its support in Provider attributes. This
behavior allows Consumer full control of the local_iov content after
dat_srq_post_recv() returns. Because this behavior is not guaranteed by
all Providers, portable Consumers shall not rely on this behavior.
Consumers shall not rely on the Provider copying local_iov information.

The DAT_SUCCESS return of the dat_srq_post_recv() is at least the
equivalent of posting a Receive operation directly by native Transport.
Providers shall avoid resource allocation as part of dat_srq_post_recv()
to ensure that this operation is nonblocking.

The completion of the Receive posted to the SRQ is equivalent to what
happened to the Receive posted to the Endpoint for the Endpoint that
dequeued the Receive buffer from the Shared Receive queue.

The posted Recv DTO will complete with signal, equivalently to the
completion of Recv posted directly to the Endpoint that dequeued the Recv
buffer from SRQ with DAT_COMPLETION_UNSIGNALLED_FLAG value not set for

The posted Recv DTOs will complete in the order of Send postings to the
other endpoint of each connection whose local EP uses SRQ. There is no
ordering among different connections regardless if they share SRQ and
recv_evd or not.

If the reported status of the Completion DTO event corresponding to the
posted RDMA Read DTO is not DAT_DTO_SUCCESS, the content of the local_iov
is not defined and the transfered_length in the DTO Completion event is
not defined.

The operation is valid for all states of the Shared Receive Queue.

The dat_srq_post_recv() function is asynchronous, nonblocking, and its
thread safety is Provider-dependent.


The operation was successful.

The srq_handle argument is an invalid DAT

The operation failed due to resource

Invalid parameter. For example, one of the
IOV segments pointed to a memory outside
its LMR.

Protection violation for local or remote
memory access.

Protection Zone mismatch between an LMR of
one of the local_iov segments and the SRQ.

Privileges violation for local or remote
memory access. One of the LMRs used in
local_iov was either invalid or did not
have the local write privileges.


For the best Recv operation performance, the Consumer should align each
buffer segment of local_iov to the Optimal Buffer Alignment attribute of
the Provider. For portable applications, the Consumer should align each
buffer segment of local_iov to the DAT_OPTIMAL_ALIGNMENT.

Since any of the Endpoints that use the SRQ can dequeue the posted buffer
from SRQ, Consumers should post a buffer large enough to handle incoming
message on any of these Endpoint connections.

The buffer posted to SRQ does not have a DTO completion flag value.
Posting Recv buffer to SRQ is semantically equivalent to posting to EP
with DAT_COMPLETION_UNSIGNALLED_FLAG is not set. The configuration of the
Recv Completion flag of an Endpoint that dequeues the posted buffer
defines how DTO completion is generated. If the Endpoint Recv Completion
completion flag value for Solicited Wait determines if the completion
will be Signalled or not. If the Endpoint Recv Completion flag is not
DAT_COMPLETION_SOLICITED_WAIT_FLAG, the posted Recv completion will be
generated with Signal. If the Endpoint Recv Completion flag is
DAT_COMPLETION_EVD_THRESHOLD_FLAG, the posted Recv completion will be
generated with Signal and dat_evd_wait threshold value controls if the
waiter will be unblocked or not.

Only the Endpoint that is in Connected or Disconnect Pending states can
dequeue buffers from SRQ. When an Endpoint is transitioned into
Disconnected state, all the buffers that it dequeued from SRQ are queued
on the Endpoint recv_evd. All the buffers that the Endpoint has not
completed by the time of transition into Disconnected state and that have
not completed message reception will be flushed.


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

|Interface Stability | Standard: uDAPL, 1.2 |
|MT-Level | Unsafe |


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

July 16, 2004 DAT_SRQ_POST_RECV(3DAT)