Implement a RecursiveMutex class which is an explicit Recursive Mutex. Change the db mutex to a recursive Mutex

src/zm_db.cpp

@@ -24,7 +24,7 @@
 #include "zm_db.h"
 
 MYSQL dbconn;
-Mutex db_mutex;
+RecursiveMutex db_mutex;
 
 bool zmDbConnected = false;
 
@@ -98,8 +98,8 @@ MYSQL_RES * zmDbFetch(const char * query) {
   db_mutex.lock();
 
   if ( mysql_query(&dbconn, query) ) {
-    Error("Can't run query: %s", mysql_error(&dbconn));
     db_mutex.unlock();
+    Error("Can't run query: %s", mysql_error(&dbconn));
     return NULL;
   }
   Debug(4, "Success running query: %s", query);

src/zm_db.h

@@ -41,7 +41,7 @@ class zmDbRow {
 };
 
 extern MYSQL dbconn;
-extern Mutex db_mutex;
+extern RecursiveMutex db_mutex;
 
 bool zmDbConnect();
 void zmDbClose();

src/zm_thread.cpp

@@ -95,6 +95,15 @@ bool Mutex::locked() {
   return( state == EBUSY );
 }
 
+RecursiveMutex::RecursiveMutex() {
+  pthread_mutexattr_t attr;
+  pthread_mutexattr_init(&attr);
+  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+
+  if ( pthread_mutex_init(&mMutex, &attr) < 0 )
+    Error("Unable to create pthread mutex: %s", strerror(errno));
+}
+
 Condition::Condition( Mutex &mutex ) : mMutex( mutex ) {
   if ( pthread_cond_init( &mCondition, NULL ) < 0 )
     throw ThreadException( stringtf( "Unable to create pthread condition: %s", strerror(errno) ) );

src/zm_thread.h

@@ -70,7 +70,7 @@ public:
 
   private:
     pthread_mutex_t *getMutex() {
-    return( &mMutex );
+      return &mMutex;
     }
 
   public:
@@ -82,6 +82,13 @@ public:
     bool locked();
 };
 
+class RecursiveMutex : public Mutex {
+  private:
+    pthread_mutex_t mMutex;
+  public:
+    RecursiveMutex();
+};
+
 class ScopedMutex {
 private:
   Mutex &mMutex;