Provided by: libfabric-dev_1.5.3-1_amd64 
NAME
fi_poll - Polling and wait set operations
fi_poll_open / fi_close : Open/close a polling set
fi_poll_add / fi_poll_del : Add/remove a completion queue or counter to/from a poll set.
fi_poll : Poll for progress and events across multiple completion queues and counters.
fi_wait_open / fi_close : Open/close a wait set
fi_wait : Waits for one or more wait objects in a set to be signaled.
fi_trywait : Indicate when it is safe to block on wait objects using native OS calls.
fi_control : Control wait set operation or attributes.
SYNOPSIS
#include <rdma/fi_domain.h>
int fi_poll_open(struct fid_domain *domain, struct fi_poll_attr *attr,
struct fid_poll **pollset);
int fi_close(struct fid *pollset);
int fi_poll_add(struct fid_poll *pollset, struct fid *event_fid,
uint64_t flags);
int fi_poll_del(struct fid_poll *pollset, struct fid *event_fid,
uint64_t flags);
int fi_poll(struct fid_poll *pollset, void **context, int count);
int fi_wait_open(struct fid_fabric *fabric, struct fi_wait_attr *attr,
struct fid_wait **waitset);
int fi_close(struct fid *waitset);
int fi_wait(struct fid_wait *waitset, int timeout);
int fi_trywait(struct fid_fabric *fabric, struct fid **fids, size_t count);
int fi_control(struct fid *waitset, int command, void *arg);
ARGUMENTS
fabric : Fabric provider
domain : Resource domain
pollset : Event poll set
waitset : Wait object set
attr : Poll or wait set attributes
context : On success, an array of user context values associated with completion queues or counters.
fids : An array of fabric descriptors, each one associated with a native wait object.
count : Number of entries in context or fids array.
timeout : Time to wait for a signal, in milliseconds.
command : Command of control operation to perform on the wait set.
arg : Optional control argument.
DESCRIPTION
fi_poll_open
fi_poll_open creates a new polling set. A poll set enables an optimized method for progressing
asynchronous operations across multiple completion queues and counters and checking for their
completions.
A poll set is defined with the following attributes.
struct fi_poll_attr {
uint64_t flags; /* operation flags */
};
flags : Flags that set the default operation of the poll set. The use of this field is reserved and must
be set to 0 by the caller.
fi_close
The fi_close call releases all resources associated with a poll set. The poll set must not be associated
with any other resources prior to being closed, otherwise the call will return -FI_EBUSY.
fi_poll_add
Associates a completion queue or counter with a poll set.
fi_poll_del
Removes a completion queue or counter from a poll set.
fi_poll
Progresses all completion queues and counters associated with a poll set and checks for events. If
events might have occurred, contexts associated with the completion queues and/or counters are returned.
Completion queues will return their context if they are not empty. The context associated with a counter
will be returned if the counter's success value or error value have changed since the last time fi_poll,
fi_cntr_set, or fi_cntr_add were called. The number of contexts is limited to the size of the context
array, indicated by the count parameter.
Note that fi_poll only indicates that events might be available. In some cases, providers may consume
such events internally, to drive progress, for example. This can result in fi_poll returning false
positives. Applications should drive their progress based on the results of reading events from a
completion queue or reading counter values. The fi_poll function will always return all completion
queues and counters that do have new events.
fi_wait_open
fi_wait_open allocates a new wait set. A wait set enables an optimized method of waiting for events
across multiple completion queues and counters. Where possible, a wait set uses a single underlying wait
object that is signaled when a specified condition occurs on an associated completion queue or counter.
The properties and behavior of a wait set are defined by struct fi_wait_attr.
struct fi_wait_attr {
enum fi_wait_obj wait_obj; /* requested wait object */
uint64_t flags; /* operation flags */
};
wait_obj : Wait sets are associated with specific wait object(s). Wait objects allow applications to
block until the wait object is signaled, indicating that an event is available to be read. The following
values may be used to specify the type of wait object associated with a wait set: FI_WAIT_UNSPEC,
FI_WAIT_FD, and FI_WAIT_MUTEX_COND.
• FI_WAIT_UNSPEC : Specifies that the user will only wait on the wait set using fabric interface calls,
such as fi_wait. In this case, the underlying provider may select the most appropriate or highest
performing wait object available, including custom wait mechanisms. Applications that select
FI_WAIT_UNSPEC are not guaranteed to retrieve the underlying wait object.
• FI_WAIT_FD : Indicates that the wait set should use file descriptor(s) as its wait mechanism. It may
not always be possible for a wait set to be implemented using a single underlying file descriptor, but
all wait objects will be file descriptors. File descriptor wait objects must be usable in the POSIX
select(2), poll(2), and epoll(7) routines (if available). However, a provider may signal an FD wait
object by marking it as readable or with an error.
• FI_WAIT_MUTEX_COND : Specifies that the wait set should use a pthread mutex and cond variable as a wait
object.
• FI_WAIT_CRITSEC_COND : Windows specific. Specifies that the EQ should use a critical section and
condition variable as a wait object.
flags : Flags that set the default operation of the wait set. The use of this field is reserved and must
be set to 0 by the caller.
fi_close
The fi_close call releases all resources associated with a wait set. The wait set must not be bound to
any other opened resources prior to being closed, otherwise the call will return -FI_EBUSY.
fi_wait
Waits on a wait set until one or more of its underlying wait objects is signaled.
fi_trywait
The fi_trywait call was introduced in libfabric version 1.3. The behavior of using native wait objects
without the use of fi_trywait is provider specific and should be considered non-deterministic.
The fi_trywait() call is used in conjunction with native operating system calls to block on wait objects,
such as file descriptors. The application must call fi_trywait and obtain a return value of FI_SUCCESS
prior to blocking on a native wait object. Failure to do so may result in the wait object not being
signaled, and the application not observing the desired events. The following pseudo-code demonstrates
the use of fi_trywait in conjunction with the OS select(2) call.
fi_control(&cq->fid, FI_GETWAIT, (void *) &fd);
FD_ZERO(&fds);
FD_SET(fd, &fds);
while (1) {
if (fi_trywait(&cq, 1) == FI_SUCCESS)
select(fd + 1, &fds, NULL, &fds, &timeout);
do {
ret = fi_cq_read(cq, &comp, 1);
} while (ret > 0);
}
fi_trywait() will return FI_SUCCESS if it is safe to block on the wait object(s) corresponding to the
fabric descriptor(s), or -FI_EAGAIN if there are events queued on the fabric descriptor or if blocking
could hang the application.
The call takes an array of fabric descriptors. For each wait object that will be passed to the native
wait routine, the corresponding fabric descriptor should first be passed to fi_trywait. All fabric
descriptors passed into a single fi_trywait call must make use of the same underlying wait object type.
The following types of fabric descriptors may be passed into fi_trywait: event queues, completion queues,
counters, and wait sets. Applications that wish to use native wait calls should select specific wait
objects when allocating such resources. For example, by setting the item's creation attribute wait_obj
value to FI_WAIT_FD.
In the case the wait object to check belongs to a wait set, only the wait set itself needs to be passed
into fi_trywait. The fabric resources associated with the wait set do not.
On receiving a return value of -FI_EAGAIN from fi_trywait, an application should read all queued
completions and events, and call fi_trywait again before attempting to block. Applications can make use
of a fabric poll set to identify completion queues and counters that may require processing.
fi_control
The fi_control call is used to access provider or implementation specific details of the wait set.
Access to the wait set should be serialized across all calls when fi_control is invoked, as it may
redirect the implementation of wait set operations. The following control commands are usable with a
wait set.
FI_GETWAIT (void **) : This command allows the user to retrieve the low-level wait object associated with
the wait set. The format of the wait set is specified during wait set creation, through the wait set
attributes. The fi_control arg parameter should be an address where a pointer to the returned wait
object will be written. This should be an 'int *' for FI_WAIT_FD, or 'struct fi_mutex_cond' for
FI_WAIT_MUTEX_COND. Support for FI_GETWAIT is provider specific and may fail if not supported or if the
wait set is implemented using more than one wait object.
RETURN VALUES
Returns FI_SUCCESS on success. On error, a negative value corresponding to fabric errno is returned.
Fabric errno values are defined in rdma/fi_errno.h.
fi_poll : On success, if events are available, returns the number of entries written to the context
array.
NOTES
SEE ALSO
fi_getinfo(3), fi_domain(3), fi_cntr(3), fi_eq(3)
AUTHORS
OpenFabrics.