Function sts_initialize

src/backend/utils/sort/sharedtuplestore.c:126–171

* Initialize a SharedTuplestore in existing shared memory. There must be * space for sts_estimate(participants) bytes. If flags includes the value * SHARED_TUPLESTORE_SINGLE_PASS, the files may in future be removed more * eagerly (but this isn't yet implemented). * * Tuples that are stored may optionally carry a piece of fixed sized * meta-data which will be retrieved along with the tuple.

 * across all SharedTuplestores created in the same SharedFileSet.
 */
SharedTuplestoreAccessor *
sts_initialize(SharedTuplestore *sts, int participants,
			   int my_participant_number,
			   size_t meta_data_size,
			   int flags,
			   SharedFileSet *fileset,
			   const char *name)
{
	SharedTuplestoreAccessor *accessor;
	int			i;

	Assert(my_participant_number < participants);

	sts->nparticipants = participants;
	sts->meta_data_size = meta_data_size;
	sts->flags = flags;

	if (strlen(name) > sizeof(sts->name) - 1)
		elog(ERROR, "SharedTuplestore name too long");
	strcpy(sts->name, name);

	/*
	 * Limit meta-data so it + tuple size always fits into a single chunk.
	 * sts_puttuple() and sts_read_tuple() could be made to support scenarios
	 * where that's not the case, but it's not currently required. If so,
	 * meta-data size probably should be made variable, too.
	 */
	if (meta_data_size + sizeof(uint32) >= STS_CHUNK_DATA_SIZE)
		elog(ERROR, "meta-data too long");

	for (i = 0; i < participants; ++i)
	{
		LWLockInitialize(&sts->participants[i].lock,
						 LWTRANCHE_SHARED_TUPLESTORE);
		sts->participants[i].read_page = 0;
		sts->participants[i].writing = false;
	}

	accessor = palloc0(sizeof(SharedTuplestoreAccessor));
	accessor->participant = my_participant_number;
	accessor->sts = sts;
	accessor->fileset = fileset;
	accessor->context = CurrentMemoryContext;

	return accessor;
}

/*
 * Attach to a SharedTuplestore that has been initialized by another backend,