rough in a db queue thread. Use it in zm_logger so that we don't have to aquire the db lock

src/zm_db.cpp

@@ -24,6 +24,7 @@
 
 MYSQL dbconn;
 RecursiveMutex db_mutex;
+zmDbQueue   dbQueue;
 
 bool zmDbConnected = false;
 
@@ -214,3 +215,36 @@ zmDbRow::~zmDbRow() {
   }
   row = nullptr;
 }
+
+zmDbQueue::zmDbQueue() :
+  mThread(&zmDbQueue::process, this),
+  mTerminate(false)
+{ }
+
+zmDbQueue::~zmDbQueue() {
+  mTerminate = true;
+  mCondition.notify_all();
+  mThread.join();
+}
+void zmDbQueue::process() {
+  std::unique_lock<std::mutex> lock(mMutex);
+
+  while (!mTerminate and !zm_terminate) { 
+    if (mQueue.empty()) {
+      mCondition.wait(lock);
+    }
+    if (!mQueue.empty()) {
+      std::string sql = mQueue.front();
+      mQueue.pop();
+      lock.unlock();
+      zmDbDo(sql.c_str());
+      lock.lock();
+    }
+  }
+}  // end void zmDbQueue::process()
+
+void zmDbQueue::push(std::string sql) {
+  std::unique_lock<std::mutex> lock(mMutex);
+  mQueue.push(sql);
+  mCondition.notify_all();
+}

src/zm_db.h

@@ -23,6 +23,26 @@
 #include "zm_thread.h"
 #include <mysql/mysql.h>
 #include <mysql/mysqld_error.h>
+#include <string>
+#include <thread>
+#include <queue>
+#include <condition_variable>
+#include <mutex>
+
+class zmDbQueue {
+  private:
+  std::queue<std::string> mQueue;
+  std::thread             mThread;
+  std::mutex              mMutex;
+  std::condition_variable mCondition;
+  bool                    mTerminate;
+  public:
+  zmDbQueue();
+  ~zmDbQueue();
+  void push(const char *sql) { return push(std::string(sql)); };
+  void push(std::string);
+  void process();
+};
 
 class zmDbRow {
   private:
@@ -43,6 +63,7 @@ class zmDbRow {
 
 extern MYSQL dbconn;
 extern RecursiveMutex db_mutex;
+extern zmDbQueue  dbQueue;
 
 extern bool zmDbConnected;
 
@@ -51,7 +72,7 @@ void zmDbClose();
 int zmDbDo(const char *query);
 int zmDbDoInsert(const char *query);
 
-MYSQL_RES * zmDbFetch( const char *query );
-zmDbRow *zmDbFetchOne( const char *query );
+MYSQL_RES * zmDbFetch(const char *query);
+zmDbRow *zmDbFetchOne(const char *query);
 
 #endif // ZM_DB_H

src/zm_logger.cpp

@@ -535,32 +535,18 @@ void Logger::logPrint(bool hex, const char * const filepath, const int line, con
   }  // end if level <= mFileLevel
 
   if ( level <= mDatabaseLevel ) {
-    if (db_mutex.try_lock()) {
     int syslogSize = syslogEnd-syslogStart;
     char escapedString[(syslogSize*2)+1];
     mysql_real_escape_string(&dbconn, escapedString, syslogStart, syslogSize);
 
-      char sql[ZM_SQL_MED_BUFSIZ];
-      snprintf(sql, sizeof(sql),
+    std::string sql_string = stringtf(
         "INSERT INTO `Logs` "
         "( `TimeKey`, `Component`, `ServerId`, `Pid`, `Level`, `Code`, `Message`, `File`, `Line` )"
         " VALUES "
         "( %ld.%06ld, '%s', %d, %d, %d, '%s', '%s', '%s', %d )",
         timeVal.tv_sec, timeVal.tv_usec, mId.c_str(), staticConfig.SERVER_ID, tid, level, classString, escapedString, file, line
         );
-      if ( mysql_query(&dbconn, sql) ) {
-        Level tempDatabaseLevel = mDatabaseLevel;
-        databaseLevel(NOLOG);
-        Error("Can't insert log entry: sql(%s) error(%s)", sql, mysql_error(&dbconn));
-        databaseLevel(tempDatabaseLevel);
-      }
-      db_mutex.unlock();
-    } else {
-      Level tempDatabaseLevel = mDatabaseLevel;
-      databaseLevel(NOLOG);
-      Error("Can't insert log entry since the DB lock could not be obtained. Message: %s", syslogStart);
-      databaseLevel(tempDatabaseLevel);
-    }
+    dbQueue.push(sql_string);
   }  // end if level <= mDatabaseLevel
 
   if ( level <= mSyslogLevel ) {