flux_kvs_commit(3)

SYNOPSIS

#include <flux/core.h>
flux_future_t *flux_kvs_commit (flux_t *h,
                                const char *ns,
                                int flags,
                                flux_kvs_txn_t *txn);
flux_future_t *flux_kvs_fence (flux_t *h,
                               const char *ns,
                               int flags,
                               const char *name,
                               int nprocs,
                               flux_kvs_txn_t *txn);
int flux_kvs_commit_get_treeobj (flux_future_t *f,
                                 const char **treeobj);
int flux_kvs_commit_get_sequence (flux_future_t *f,
                                  int *seq);

DESCRIPTION

flux_kvs_commit() sends a request via handle h to the KVS service to commit a transaction txn. txn is created with flux_kvs_txn_create(3) and after commit completion, is destroyed with flux_kvs_txn_destroy(). A flux_future_t object is returned, which acts as handle for synchronization and container for the response. The txn will operate in the namespace specified by ns. If ns is NULL, flux_kvs_commit() will operate on the default namespace, or if set, the namespace from the FLUX_KVS_NAMESPACE environment variable. Note that all transactions operate on the same namespace.

flux_kvs_fence() is a "collective" version of flux_kvs_commit() that supports multiple callers. Each caller uses the same flags, name, and nprocs arguments. Once nprocs requests are received by the KVS service for the named operation, the transactions are combined and committed together as one transaction. name must be unique across the Flux session and should not be reused, even after the fence is complete.

flux_future_then(3) may be used to register a reactor callback (continuation) to be called once the response to the commit/fence request has been received. flux_future_wait_for(3) may be used to block until the response has been received. Both accept an optional timeout.

flux_future_get(), flux_kvs_commit_get_treeobj(), or flux_kvs_commit_get_sequence() can decode the response. A return of 0 indicates success and the entire transaction was committed. A return of -1 indicates failure, none of the transaction was committed. All can be used on the flux_future_t returned by flux_kvs_commit() or flux_kvs_fence().

In addition to checking for success or failure, flux_kvs_commit_get_treeobj() and flux_kvs_commit_get_sequence() can return information about the root snapshot that the commit or fence has completed its transaction on.

flux_kvs_commit_get_treeobj() obtains the root hash in the form of an RFC 11 dirref treeobj, suitable to be passed to flux_kvs_lookupat(3).

flux_kvs_commit_get_sequence() retrieves the monotonic sequence number for the root.

FLAGS

The following are valid bits in a flags mask passed as an argument to flux_kvs_commit() or flux_kvs_fence().

FLUX_KVS_NO_MERGE
The KVS service may merge contemporaneous commit transactions as an optimization. However, if the combined transactions modify the same key, a watch on that key may only be notified of the last-in value. This flag can be used to disable that optimization for this transaction.

RETURN VALUE

flux_kvs_commit() and flux_kvs_fence() return a flux_future_t on success, or NULL on failure with errno set appropriately.

ERRORS

EINVAL
One of the arguments was invalid.
ENOMEM
Out of memory.
EPROTO
A request was malformed.
ENOSYS
The KVS module is not loaded.
ENOTSUP
An unknown namespace was requested.
EOVERFLOW
flux_kvs_fence() has been called too many times and nprocs has been exceeded.

SEE ALSO

flux_future_get(3), flux_kvs_txn_create(3), flux_kvs_set_namespace(3)