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:

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)