Use async name resolving to improve net thread responsiveness

In the LookupIntern(), things changed are:

  1. Call getaddrinfo_a() instead of getaddrinfo() if available, the former is a sync version of the latter;
  2. Try using inet_pton()/inet_addr() to convert the input text to a network addr structure at first, if success the extra name resolving thread inside getaddrinfo_a() could be avoided;
  3.  An interruption point added in the waiting loop for return from getaddrinfo_a(), which completes the improve for thread responsiveness.

A easy way to see the effect is to kick off a 'bitcoind stop' immediately after 'bitcoind -daemon', before the change it would take several, or even tens of, minutes on a bad network situation to wait for the running bitcoind to exit, now it costs only seconds.

Signed-off-by: Huang Le <4tarhl@gmail.com>

configure.ac

@@ -369,6 +369,8 @@ if test x$TARGET_OS = xdarwin; then
 fi
 
 AC_CHECK_HEADERS([endian.h stdio.h stdlib.h unistd.h strings.h sys/types.h sys/stat.h sys/select.h])
+AC_SEARCH_LIBS([getaddrinfo_a], [anl], [AC_DEFINE(HAVE_GETADDRINFO_A, 1, [Define this symbol if you have getaddrinfo_a])])
+AC_SEARCH_LIBS([inet_pton], [nsl resolv], [AC_DEFINE(HAVE_INET_PTON, 1, [Define this symbol if you have inet_pton])])
 
 AC_CHECK_DECLS([le32toh, le64toh, htole32, htole64, be32toh, be64toh, htobe32, htobe64],,,
 		[#if HAVE_ENDIAN_H

src/netbase.cpp

@@ -3,6 +3,18 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#ifdef HAVE_CONFIG_H
+#include "bitcoin-config.h"
+#endif
+
+#ifdef HAVE_INET_PTON
+#include <arpa/inet.h>
+#endif
+
+#ifdef HAVE_GETADDRINFO_A
+#include <netdb.h>
+#endif
+
 #include "netbase.h"
 
 #include "hash.h"
@@ -71,9 +83,30 @@ bool static LookupIntern(const char *pszName, std::vector<CNetAddr>& vIP, unsign
         }
     }
 
+#ifdef HAVE_GETADDRINFO_A
+    struct in_addr ipv4_addr;
+#ifdef HAVE_INET_PTON
+    if (inet_pton(AF_INET, pszName, &ipv4_addr) > 0) {
+        vIP.push_back(CNetAddr(ipv4_addr));
+        return true;
+    }
+
+    struct in6_addr ipv6_addr;
+    if (inet_pton(AF_INET6, pszName, &ipv6_addr) > 0) {
+        vIP.push_back(CNetAddr(ipv6_addr));
+        return true;
+    }
+#else
+    ipv4_addr.s_addr = inet_addr(pszName);
+    if (ipv4_addr.s_addr != INADDR_NONE) {
+        vIP.push_back(CNetAddr(ipv4_addr));
+        return true;
+    }
+#endif
+#endif
+
     struct addrinfo aiHint;
     memset(&aiHint, 0, sizeof(struct addrinfo));
-
     aiHint.ai_socktype = SOCK_STREAM;
     aiHint.ai_protocol = IPPROTO_TCP;
     aiHint.ai_family = AF_UNSPEC;
@@ -82,8 +115,33 @@ bool static LookupIntern(const char *pszName, std::vector<CNetAddr>& vIP, unsign
 #else
     aiHint.ai_flags = fAllowLookup ? AI_ADDRCONFIG : AI_NUMERICHOST;
 #endif
+
     struct addrinfo *aiRes = NULL;
+#ifdef HAVE_GETADDRINFO_A
+    struct gaicb gcb, *query = &gcb;
+    memset(query, 0, sizeof(struct gaicb));
+    gcb.ar_name = pszName;
+    gcb.ar_request = &aiHint;
+    int nErr = getaddrinfo_a(GAI_NOWAIT, &query, 1, NULL);
+    if (nErr)
+        return false;
+
+    do {
+        // Should set the timeout limit to a resonable value to avoid
+        // generating unnecessary checking call during the polling loop,
+        // while it can still response to stop request quick enough.
+        // 2 seconds looks fine in our situation.
+        struct timespec ts = { 2, 0 };
+        gai_suspend(&query, 1, &ts);
+        boost::this_thread::interruption_point();
+
+        nErr = gai_error(query);
+        if (0 == nErr)
+            aiRes = query->ar_result;
+    } while (nErr == EAI_INPROGRESS);
+#else
     int nErr = getaddrinfo(pszName, NULL, &aiHint, &aiRes);
+#endif
     if (nErr)
         return false;