From 61009cefc76660493b66d89721129d1b7f4c014d Mon Sep 17 00:00:00 2001
From: Eric House <eehouse@eehouse.org>
Date: Thu, 15 Aug 2013 07:24:30 -0700
Subject: [PATCH] in advance of using memcache, keep track (in memory) of those
 devids for which no messages are pending, since that's a query that can be
 made by each device every minute.

---
 xwords4/relay/dbmgr.cpp | 39 ++++++++++++++++++++++++++++++++++++---
 xwords4/relay/dbmgr.h   |  8 ++++++++
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/xwords4/relay/dbmgr.cpp b/xwords4/relay/dbmgr.cpp
index 5d3cf2524..15825c6ff 100644
--- a/xwords4/relay/dbmgr.cpp
+++ b/xwords4/relay/dbmgr.cpp
@@ -877,6 +877,8 @@ DBMgr::StoreMessage( const char* const connName, int hid,
     if ( DEVID_NONE == devID ) {
         logf( XW_LOGERROR, "%s: warning: devid not found for connName=%s, "
               "hid=%d", __func__, connName, hid );
+    } else {
+        clearHasNoMessages( devID );
     }
 
     size_t newLen;
@@ -972,9 +974,15 @@ DBMgr::storedMessagesImpl( string test, vector<DBMgr::MsgInfo>& msgs )
 void
 DBMgr::GetStoredMessages( DevIDRelay relayID, vector<MsgInfo>& msgs )
 {
-    string query;
-    string_printf( query, "devid=%d", relayID );
-    storedMessagesImpl( query, msgs );
+    if ( !hasNoMessages( relayID ) ) {
+        string query;
+        string_printf( query, "devid=%d", relayID );
+        storedMessagesImpl( query, msgs );
+
+        if ( 0 == msgs.size() ) {
+            setHasNoMessages( relayID );
+        }
+    }
 }
 
 void
@@ -1058,6 +1066,31 @@ DBMgr::getCountWhere( const char* table, string& test )
     return count;
 }
 
+bool DBMgr::hasNoMessages( DevIDRelay devid )
+{
+    bool result;
+    {
+        MutexLock ml( &m_haveNoMessagesMutex );
+        result = m_haveNoMessages.find(devid) != m_haveNoMessages.end();
+    }
+    logf( XW_LOGINFO, "%s(devid=%d)=>%d", __func__, devid, result );
+    return result;
+}
+
+void DBMgr::setHasNoMessages( DevIDRelay devid )
+{
+    logf( XW_LOGINFO, "%s(devid=%d)", __func__, devid );
+    MutexLock ml( &m_haveNoMessagesMutex );
+    m_haveNoMessages.insert( devid );
+}
+
+void DBMgr::clearHasNoMessages( DevIDRelay devid )
+{
+    logf( XW_LOGINFO, "%s(devid=%d)", __func__, devid );
+    MutexLock ml( &m_haveNoMessagesMutex );
+    m_haveNoMessages.erase( devid );
+}
+
 static void
 formatParams( char* paramValues[], int nParams, const char* fmt, char* buf, 
               int bufLen, ... )
diff --git a/xwords4/relay/dbmgr.h b/xwords4/relay/dbmgr.h
index ae79335c2..3b629999a 100644
--- a/xwords4/relay/dbmgr.h
+++ b/xwords4/relay/dbmgr.h
@@ -23,6 +23,7 @@
 #define _DBMGR_H_
 
 #include <string>
+#include <set>
 
 #include "xwrelay.h"
 #include "xwrelay_priv.h"
@@ -141,10 +142,17 @@ class DBMgr {
     PGconn* getThreadConn( void );
     void clearThreadConn();
 
+    bool hasNoMessages( DevIDRelay devid );
+    void setHasNoMessages( DevIDRelay devid );
+    void clearHasNoMessages( DevIDRelay devid );
+
     void conn_key_alloc();
     pthread_key_t m_conn_key;
     bool m_useB64;
 
+    pthread_mutex_t m_haveNoMessagesMutex;
+    set<DevIDRelay> m_haveNoMessages;
+
 }; /* DBMgr */