From c9a772e36bd27bb0c78fef9b90f90eb5a55b4e00 Mon Sep 17 00:00:00 2001
From: Robert James Kaes <rjkaes@users.sourceforge.net>
Date: Wed, 29 Aug 2001 03:57:51 +0000
Subject: Added a more fine grained locking system for multiple threads.
 Removed the new_dnscache() function and moved it into dnscache(). Fixed a
 memory leak in dns_insert().

---
 src/dnscache.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 78 insertions(+), 14 deletions(-)

diff --git a/src/dnscache.c b/src/dnscache.c
index 8ec3b69..6ff89f1 100644
--- a/src/dnscache.c
+++ b/src/dnscache.c
@@ -1,4 +1,4 @@
-/* $Id: dnscache.c,v 1.9 2001-05-27 02:24:00 rjkaes Exp $
+/* $Id: dnscache.c,v 1.10 2001-08-29 03:57:51 rjkaes Exp $
  *
  * This is a caching DNS system. When a host name is needed we look it up here
  * and see if there is already an answer for it. The domains are placed in a
@@ -34,6 +34,14 @@
 #include "ternary.h"
 #include "utils.h"
 
+/*
+ * The mutex is used for locking around accesses to the ternary tree.
+ */
+static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+
+#define LOCK()   pthread_mutex_lock(&mutex);
+#define UNLOCK() pthread_mutex_unlock(&mutex);
+
 #define DNSEXPIRE (5 * 60)
 
 struct dnscache_s {
@@ -41,49 +49,94 @@ struct dnscache_s {
 	time_t expire;
 };
 
-static TERNARY dns_tree;
+static TERNARY dns_tree = -1;
 
-TERNARY new_dnscache(void)
+/*
+ * Insert the data into the DNS tree.
+ */
+static int insert_data(char *domain, struct dnscache_s *newptr)
 {
-	dns_tree = ternary_new();
+	int ret;
+	
+	LOCK();
+	ret = ternary_insert(dns_tree, domain, newptr);
+	UNLOCK();
 
-	return dns_tree;
+	return ret;
 }
 
 static int dns_lookup(struct in_addr *addr, char *domain)
 {
+	int ret;
 	struct dnscache_s *ptr;
 
 	assert(addr != NULL);
 	assert(domain != NULL);
 
-	if (TE_ISERROR(ternary_search(dns_tree, domain, (void *)&ptr))) 
-		return -1;
+	LOCK();
+	ret = ternary_search(dns_tree, domain, (void *)&ptr);
 
-	if (difftime(time(NULL), ptr->expire) > (double)DNSEXPIRE) {
+	if (TE_ISERROR(ret)
+	    || difftime(time(NULL), ptr->expire) > DNSEXPIRE) {
+		UNLOCK();
 		return -1;
 	}
 
-	*addr = ptr->ipaddr;
+	memcpy(addr, &ptr->ipaddr, sizeof(struct in_addr));
+	UNLOCK();
+
 	return 0;
 }
 
 static int dns_insert(struct in_addr *addr, char *domain)
 {
 	struct dnscache_s *newptr;
+	int ret;
 
 	assert(addr != NULL);
 	assert(domain != NULL);
 
+	DEBUG2("Inserting [%s] into DNS cache", domain);
+
 	if (!(newptr = malloc(sizeof(struct dnscache_s)))) {
 		return -1;
 	}
 
-	newptr->ipaddr = *addr;
+	memcpy(&newptr->ipaddr, addr, sizeof(struct in_addr));
 	newptr->expire = time(NULL);
 
-	if (TE_ISERROR(ternary_insert(dns_tree, domain, newptr)))
-		safefree(newptr);
+	ret = insert_data(domain, newptr);
+
+	if (TE_ISERROR(ret)) {
+		if (ret == TE_EXISTS) {
+			/*
+			 * The value already exists. First search for the
+			 * value and then delete the data before inserting
+			 * the new value.
+			 */
+			struct dnscache_s *existing;
+
+			DEBUG2("[%s] already exists in DNS cache", domain);
+
+			LOCK();
+			ret = ternary_search(dns_tree, domain, (void *)&existing);
+			UNLOCK();
+
+			if (TE_ISERROR(ret))
+				goto INSERT_ERROR;
+
+			safefree(existing);
+
+			ret = insert_data(domain, newptr);
+
+			if (TE_ISERROR(ret))
+				goto INSERT_ERROR;
+		} else {
+		INSERT_ERROR:
+			safefree(newptr);
+			return -1;
+		}
+	}
 
 	return 0;
 }
@@ -95,7 +148,13 @@ int dnscache(struct in_addr *addr, char *domain)
 	assert(addr != NULL);
 	assert(domain != NULL);
 
-	if (inet_aton(domain, (struct in_addr *) addr) != 0)
+	/* If the DNS tree doesn't exist, build a new one */
+	LOCK();
+	if (dns_tree < 0)
+		dns_tree = ternary_new();
+	UNLOCK();
+
+	if (inet_aton(domain, (struct in_addr *)addr) != 0)
 		return 0;
 
 	/* Well, we're not dotted-decimal so we need to look it up */
@@ -103,10 +162,15 @@ int dnscache(struct in_addr *addr, char *domain)
 		return 0;
 
 	/* Okay, so not in the list... need to actually look it up. */
-	if (!(resolv = gethostbyname(domain)))
+	LOCK();
+	if (!(resolv = gethostbyname(domain))) {
+		UNLOCK();
 		return -1;
+	}
 
 	memcpy(addr, resolv->h_addr_list[0], (size_t)resolv->h_length);
+	UNLOCK();
+
 	dns_insert(addr, domain);
 
 	return 0;
-- 
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