Handle DB-locked errors.

When multiple processes (right now, multiple copies of fgfs, but potentially other users in the future) access the navcache, it can cause SQLite to return a 'locked' error, so the request should be re-tried. Add code to do this.

diff --git a/src/Navaids/NavDataCache.cxx b/src/Navaids/NavDataCache.cxx
index e6eb1827b5313cce9f4d60da4bfa1431e5fdb8ad..0e5d3e9407c150e3c9947bab2fb5445745a3ade9 100644 (file)
--- a/src/Navaids/NavDataCache.cxx
+++ b/src/Navaids/NavDataCache.cxx
@@ -334,15 +334,32 @@ public:
     return stepSelect(stmt);
   }
   
+  const int MAX_RETRIES = 10;
+  
   bool stepSelect(sqlite3_stmt_ptr stmt)
   {
-    int result = sqlite3_step(stmt);
-    if (result == SQLITE_ROW) {
-      return true; // at least one result row
-    }
+    int retries = 0;
+    int result;
+    while (retries < MAX_RETRIES) {
+      result = sqlite3_step(stmt);
+      if (result == SQLITE_ROW) {
+        return true; // at least one result row
+      }
+      
+      if (result == SQLITE_DONE) {
+        return false; // no result rows
+      }
+      
+      if (result != SQLITE_LOCKED) {
+        break;
+      }
+      
+      ++retries;
+    } // of retry loop for DB locked
     
-    if (result == SQLITE_DONE) {
-      return false; // no result rows
+    if (retries >= MAX_RETRIES) {
+      SG_LOG(SG_NAVCACHE, SG_ALERT, "exceeded maximum number of SQLITE_LOCKED retries");
+      return false;
     }
     
     string errMsg;