[iwhd] iwhd: handle a lost-then-restored mongo connection

[Jim Meyering]

commit 4a5a4c5c48a7316955d2e1bfde041351a823985a
Author: Pete Zaitcev <zaitcev(a)redhat.com&gt;
Date:   Wed Sep 21 06:45:20 2011 +0200

    iwhd: handle a lost-then-restored mongo connection
    
    If I read the code right, the intent was that client.connect() reset
    the .failed flag.  But actually it does not.  So, although we actually
    reconnect, isFailed() always evaluates to true and we get no cursor.
    Unfortunately, it seems that there is NO WAY to reset .failed, except
    through checkConnect(), and that 1) works only if auto-reconnect is
    enabled, and 2) is not a public method.  It is called by query()
    itself though.
    
    This patch deals with all this simply by enabling auto-reconnect,
    which basically does exactly what we did explicitly before, only it
    happens inside query() now.
    * meta.cpp: Handle SocketException, too
    
    However, this is not the complete solution.  Further testing suggests
    that if you bombard iwhd with requests when mongo is not responding,
    eventually, iwhd will crash.

 meta.cpp |   46 ++++++++++++++++++++++------------------------
 1 files changed, 22 insertions(+), 24 deletions(-)
---
diff --git a/meta.cpp b/meta.cpp
index 7b3a5d7..fa2c591 100644
--- a/meta.cpp
+++ b/meta.cpp
@@ -118,7 +118,8 @@ public:
 
 static RepoMeta *it;
 
-RepoMeta::RepoMeta ()
+RepoMeta::RepoMeta () :
+    client(true)
 {
 	if (!verbose) {
 		cout.rdbuf(0);
@@ -155,27 +156,18 @@ auto_ptr<DBClientCursor>
 RepoMeta::GetCursor (Query &q)
 {
 	auto_ptr<DBClientCursor> curs;
-	bool looping = false;
-
-	for (;;) {
-		if (!client.isFailed()) {
-		        curs = client.query(MAIN_TBL,q);
-		        if (curs.get()) {
-		                break;
-		        }
-		}
-		if (looping) {
-		        break;
-		}
-		try {
-		        client.connect(addr);
-		}
-		catch (ConnectException &ce) {
-		        log_msg(IW_LOG_INFO, "reconnection to %s failed", addr);
-		}
-		looping = true;
-	}
 
+	try {
+		curs = client.query(MAIN_TBL,q);
+	}
+	catch (ConnectException &ce) {
+		log_msg(IW_LOG_INFO, "reconnection to %s failed", addr);
+		curs.reset();
+	}
+	catch (SocketException &ce) {
+		log_msg(IW_LOG_INFO, "reconnection to %s failed", addr);
+		curs.reset();
+	}
 	return curs;
 }
 
@@ -434,7 +426,13 @@ RepoQuery::RepoQuery (const char *bucket, const char *key, const char
*qstr,
 		expr = NULL;
 	}
 
-	curs = parent.GetCursor(q).release();
+	tmp = parent.GetCursor(q);
+	if (!tmp.get()) {
+		/* TBD: What to do if this happens? */
+		log_msg(IW_LOG_INFO, "no cursor");
+		return;
+	}
+	curs = tmp.release();
 	bucket = NULL;
 	key = NULL;
 }
@@ -582,7 +580,7 @@ RepoMeta::GetSize (const char *bucket, const char *key)
 
 	q = QUERY("_bucket"<<bucket<<"_key"<<key);
 	curs = GetCursor(q);
-
+	/* TBD: What to do if GetCursor() fails to reconnect? */
 	if (!curs->more()) {
 		return 0;
 	}
@@ -651,7 +649,7 @@ RepoMeta::GetAttrList (const char *bucket, const char *key)
 
 	q = QUERY("_bucket"<<bucket<<"_key"<<key);
 	curs = GetCursor(q);
-
+	/* TBD: What to do if GetCursor() fails to reconnect? */
 	if (!curs->more()) {
 		return NULL;
 	}