From 84e71c86b3d86491924368fbab194decdabd76a9 Mon Sep 17 00:00:00 2001
From: Richard Fuchs <rfuchs@sipwise.com>
Date: Thu, 19 Dec 2024 15:12:14 -0400
Subject: [PATCH] MT#61368 add call_get2()

This function retrieves two calls from the global call hash while
avoiding deadlocks. This is needed because a "call_get(A) + call_get(B)"
would deadlock against a concurrent "call_get(B) + call_get(A)"

Unused at this point.

Change-Id: I95127ce1afa19386a847984ca26eb7d7368e6569
---
 daemon/call.c  | 40 ++++++++++++++++++++++++++++++++++++++++
 include/call.h |  3 +++
 2 files changed, 43 insertions(+)

diff --git a/daemon/call.c b/daemon/call.c
index 6410f555d..580a67b18 100644
--- a/daemon/call.c
+++ b/daemon/call.c
@@ -4347,6 +4347,46 @@ call_t *call_get(const str *callid) {
 	return ret;
 }
 
+// special version of call_get() to get two calls while avoiding deadlock
+call_get2_ret_t call_get2(call_t **ret1, call_t **ret2, const str *callid1, const str *callid2) {
+	call_get2_ret_t ret;
+
+	while (true) {
+		RWLOCK_R(&rtpe_callhash_lock);
+
+		*ret1 = t_hash_table_lookup(rtpe_callhash, callid1);
+		if (!*ret1)
+			return CG2_NF1;
+		*ret2 = t_hash_table_lookup(rtpe_callhash, callid2);
+		if (!*ret2)
+			return CG2_NF2;
+
+		if (*ret1 == *ret2) {
+			*ret2 = NULL;
+			ret = CG2_SAME;
+			rwlock_lock_w(&(*ret1)->master_lock);
+			obj_hold(*ret1);
+		}
+		else {
+			rwlock_lock_w(&(*ret1)->master_lock);
+			if (rwlock_trylock_w(&(*ret2)->master_lock)) {
+				// try again
+				rwlock_unlock_w(&(*ret1)->master_lock);
+				continue;
+			}
+
+			ret = CG2_OK;
+			obj_hold(*ret1);
+			obj_hold(*ret2);
+		}
+
+		break;
+	}
+
+	log_info_call(*ret1);
+	return ret;
+}
+
 static gboolean fragment_move(str *key, fragment_q *q, void *c) {
 	call_t *call = c;
 	t_hash_table_insert(call->sdp_fragments, key, q);
diff --git a/include/call.h b/include/call.h
index a3821b134..ead6cc2d8 100644
--- a/include/call.h
+++ b/include/call.h
@@ -833,6 +833,9 @@ struct call_monologue *call_get_monologue(call_t *call, const str *fromtag);
 struct call_monologue *call_get_or_create_monologue(call_t *call, const str *fromtag);
 __attribute__((nonnull(1)))
 call_t *call_get(const str *callid);
+typedef enum { CG2_OK, CG2_NF1, CG2_NF2, CG2_SAME } call_get2_ret_t;
+__attribute__((nonnull(1, 2, 3, 4)))
+call_get2_ret_t call_get2(call_t **, call_t **, const str *, const str *);
 __attribute__((nonnull(1, 2)))
 bool call_merge(call_t *, call_t **);
 __attribute__((nonnull(2, 3)))