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Support for off-loop read-ony qp-trie transactions

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It is sometimes necessary to access a qp-trie outside an isc_loop,
such as in tests or an isc_work callback. The best option was to use
a `dns_qpmulti_write()` transaction, but that has overheads that are
not necessary for read-only access, such as committing a new version
of the trie even when nothing changed.

So this commit adds a `dns_qpmulti_read()` transaction, which is
nearly as lightweight as a query transaction, but it takes the mutex
like a write transaction.
This commit is contained in:
Tony Finch
2023-03-02 13:30:24 +00:00
parent fa1b57ee6e
commit 44c80c4ae1
2 changed files with 50 additions and 5 deletions
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30
lib/dns/qp.c
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@@ -1282,12 +1282,31 @@ dns_qpmulti_query(dns_qpmulti_t *multi, dns_qpread_t *qp) {
REQUIRE(QPMULTI_VALID(multi));
REQUIRE(qp != NULL);
dns_qpmulti_t *whence = reader_open(multi, qp);
INSIST(whence == multi);
/* we must be in an isc_loop thread */
/* we MUST be in an isc_loop thread */
qp->tid = isc_tid();
REQUIRE(qp->tid != ISC_TID_UNKNOWN);
dns_qpmulti_t *whence = reader_open(multi, qp);
INSIST(whence == multi);
}
/*
* a locked read takes the mutex
*/
void
dns_qpmulti_lockedread(dns_qpmulti_t *multi, dns_qpread_t *qp) {
REQUIRE(QPMULTI_VALID(multi));
REQUIRE(qp != NULL);
/* we MUST NOT be in an isc_loop thread */
qp->tid = isc_tid();
REQUIRE(qp->tid == ISC_TID_UNKNOWN);
LOCK(&multi->mutex);
dns_qpmulti_t *whence = reader_open(multi, qp);
INSIST(whence == multi);
}
void
@@ -1295,6 +1314,9 @@ dns_qpread_destroy(dns_qpmulti_t *multi, dns_qpread_t *qp) {
REQUIRE(QPMULTI_VALID(multi));
REQUIRE(QP_VALID(qp));
REQUIRE(qp->tid == isc_tid());
if (qp->tid == ISC_TID_UNKNOWN) {
UNLOCK(&multi->mutex);
}
*qp = (dns_qpread_t){};
}