[ML] Add control message to start background persistence (#19)

* Add control message for back ground persist

* Add isBusy check to public startBackgroundPersist function

* Document thread safety aspects

Author: davidkyle

include/api/CBackgroundPersister.h

@@ -47,6 +47,13 @@ namespace api
 //! are that a lot of memory is being used by the temporary
 //! copy of the data to be persisted.
 //!
+//! Persistence happens in a background thread and further
+//! persistence requests via the startBackgroundPersist*() methods
+//! will be rejected if the background thread is executing.
+//! However, calls to startBackgroundPersist() and
+//! startBackgroundPersistIfAppropriate() are not thread safe and
+//! must not be made concurrently.
+//!
 //! IMPLEMENTATION DECISIONS:\n
 //! This class expects to call a persistence function taking
 //! just the data adder as an argument.  It's easy to wrap up
@@ -107,9 +114,15 @@ class API_EXPORT CBackgroundPersister : private core::CNonCopyable
         //! called.
         bool firstProcessorPeriodicPersistFunc(const TFirstProcessorPeriodicPersistFunc &firstProcessorPeriodicPersistFunc);
 
-        //! Check whether a background persist is appropriate now, and if it is
-        //! then start it by calling the first processor periodic persist
-        //! function.
+        //! Start a background persist is one is not running.
+        //! Calls the first processor periodic persist function first.
+        //! Concurrent calls to this method are not threadsafe.
+        bool startBackgroundPersist(void);
+
+        //! If the periodic persist interval has passed since the last persist
+        //! then it is appropriate to persist now.  Start it by calling the
+        //! first processor periodic persist function.
+        //! Concurrent calls to this method are not threadsafe.
         bool startBackgroundPersistIfAppropriate(void);
 
     private:
@@ -130,6 +143,10 @@ class API_EXPORT CBackgroundPersister : private core::CNonCopyable
         };
 
     private:
+        //! Persist in the background setting the last persist time
+        //! to timeOfPersistence
+        bool startBackgroundPersist(core_t::TTime timeOfPersistence);
+
         //! When this function is called a background persistence will be
         //! triggered unless there is already one in progress.
         bool startPersist(void);

lib/api/CAnomalyJob.cc

@@ -397,6 +397,14 @@ bool CAnomalyJob::handleControlMessage(const std::string &controlMessage)
         case 'p':
             this->doForecast(controlMessage);
             break;
+        case 'w':
+            {
+                if (m_PeriodicPersister != nullptr)
+                {
+                    m_PeriodicPersister->startBackgroundPersist();
+                }
+            }
+            break;
         default:
             LOG_WARN("Ignoring unknown control message of length " <<
                      controlMessage.length() << " beginning with '" <<

lib/api/CBackgroundPersister.cc

@@ -178,6 +178,17 @@ bool CBackgroundPersister::firstProcessorPeriodicPersistFunc(const TFirstProcess
     return true;
 }
 
+bool CBackgroundPersister::startBackgroundPersist(void)
+{
+    if (this->isBusy())
+    {
+        LOG_WARN("Cannot start background persist as a previous "
+            "persist is still in progress");
+        return false;
+    }
+    return this->startBackgroundPersist(core::CTimeUtils::now());
+}
+
 bool CBackgroundPersister::startBackgroundPersistIfAppropriate(void)
 {
     core_t::TTime due(m_LastPeriodicPersistTime + m_PeriodicPersistInterval);
@@ -201,6 +212,11 @@ bool CBackgroundPersister::startBackgroundPersistIfAppropriate(void)
         return false;
     }
 
+    return this->startBackgroundPersist(now);
+}
+
+bool CBackgroundPersister::startBackgroundPersist(core_t::TTime timeOfPersistence)
+{
     bool backgroundPersistSetupOk = m_FirstProcessorPeriodicPersistFunc(*this);
     if (!backgroundPersistSetupOk)
     {
@@ -211,7 +227,7 @@ bool CBackgroundPersister::startBackgroundPersistIfAppropriate(void)
         return false;
     }
 
-    m_LastPeriodicPersistTime = now;
+    m_LastPeriodicPersistTime = timeOfPersistence;
 
     LOG_INFO("Background persist starting background thread");