man pages section 3: Extended Library Functions, Volume 1

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Updated: July 2014
 
 

dat_srq_post_recv(3DAT)

Name

dat_srq_post_recv - add receive buffers to shared receive queue

Synopsis

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

DAT_RETURN
    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
    )

Parameters

srq_handle

A handle for an instance of the SRQ.

num_segments

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

local_iov

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

user_cookie

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

Description

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 it.

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.

Return Values

DAT_SUCCESS

The operation was successful.

DAT_INVALID_HANDLE

The srq_handle argument is an invalid DAT handle.

DAT_INSUFFICIENT_RESOURCES

The operation failed due to resource limitations.

DAT_INVALID_PARAMETER

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

DAT_PROTECTION_VIOLATION

Protection violation for local or remote memory access.

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

DAT_PRIVILEGES_VIOLATION

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.

Usage

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 flag is DAT_COMPLETION_SOLICITED_WAIT_FLAG then matching Send DTO 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.

Attributes

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

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
Unsafe
Standard
uDAPL, 1.2

See Also

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)