Add infrastructure for a simple "pure C" wrapper API to DCDBLib.

Make Mont-Blanc SlurmPlugin link against this C API.

DCDBLib/Makefile

@@ -10,7 +10,8 @@ OBJS = src/connection.o \
        src/sensordatastore.o \
        src/timestamp.o \
        src/sensorconfig.o \
-       src/sensorid.o
+       src/sensorid.o \
+       src/c_api.o
 
 # List of public header files necessary to use this libray
 PUBHEADERS = $(shell find include -type f -iname "*.h")

DCDBLib/include/c_api.h

+/*
+ * c_api.h
+ *
+ *  Created on: May 27, 2015
+ *      Author: Axel Auweter
+ */
+
+/**
+ * @file
+ * @brief This file contains a reduced public API for the
+ * DCDBLib library using C instead of C++ bindings.
+ */
+
+#ifndef DCDB_C_API_H
+#define DCDB_C_API_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void dcdb_test_c_api();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* DCDB_C_API_H */

DCDBLib/include/sensordatastore.h

@@ -37,6 +37,14 @@ public:
   SensorId sensorId;
   DCDBTimeStamp timeStamp;
   uint64_t value;
+
+#if 0
+  inline bool operator == (const SensorDataStoreReading& rhs) const {
+    return (sensorId == rhs.sensorId) &&
+        (timeStamp == rhs.timeStamp) &&
+        (value == rhs.value);}
+#endif
+
 };
 
 /**
@@ -65,7 +73,7 @@ public:
     void setTTL(uint64_t ttl);
 
     /**
-     * @brief This function querie a sensor's values in
+     * @brief This function queries a sensor's values in
      *        the given time range.
      * @param result   The list where the results will be stored.
      * @param sid      The SensorId to query.
@@ -74,6 +82,16 @@ public:
      */
     void query(std::list<SensorDataStoreReading>& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end);
 
+    /**
+     * @brief This function queries the integrated value (val * sec)
+     *        of a sensor for the given time range.
+     * @param result   The resulting integrated value.
+     * @param sid      The SensorId to query.
+     * @param start    Start of the time series.
+     * @param end      End of the time series.
+     */
+    void querySum(int64_t& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end);
+
     /**
      * @brief A shortcut constructor for a SensorDataStore object
      *        that allows accessing the data store through a

DCDBLib/include/sensorid.h

@@ -109,6 +109,12 @@ public:
    */
   bool patternMatch(std::string pattern);
 
+#if 0
+  inline bool operator == (const SensorId& rhs) const {
+    return (data.raw[0] == rhs.data.raw[0]) &&
+        (data.raw[1] == rhs.data.raw[1]);}
+#endif
+
   SensorId();
   SensorId(std::string mqttTopic);
   virtual ~SensorId();

DCDBLib/include_internal/sensordatastore_internal.h

@@ -63,6 +63,16 @@ public:
    */
   void query(std::list<SensorDataStoreReading>& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end);
 
+  /**
+   * @brief This function queries the integrated value
+   *        of a sensor for the given time range.
+   * @param result   The resulting integrated value.
+   * @param sid      The SensorId to query.
+   * @param start    Start of the time series.
+   * @param end      End of the time series.
+   */
+  void querySum(int64_t& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end);
+
   /**
    * @brief This is the standard constructor of the SensorDataStoreImpl class.
    * @param csb   A CassandraBackend object to do the raw database access.

DCDBLib/src/c_api.cpp

+/*
+ * c_api.cpp
+ *
+ *  Created on: May 27, 2015
+ *      Author: Axel Auweter
+ */
+
+#include <cstdio>
+
+#include "c_api.h"
+
+void dcdb_test_c_api()
+{
+  printf("Hello from your DCDB C API.\n");
+}

DCDBLib/src/sensordatastore.cpp

@@ -151,7 +151,7 @@ void SensorDataStoreImpl::setTTL(uint64_t ttl)
  * @details
  * This function issues a regular query to the data store
  * and creates a SensorDataStoreReading object for each
- * entry which is stores in the result list.
+ * entry which is stored in the result list.
  */
 void SensorDataStoreImpl::query(std::list<SensorDataStoreReading>& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end)
 {
@@ -223,6 +223,49 @@ void SensorDataStoreImpl::query(std::list<SensorDataStoreReading>& result, Senso
   cass_prepared_free(prepared);
 }
 
+/**
+ * @details
+ * This function generates an integrated value of the time series
+ * by first querying for the result set list using query() and then
+ * summing up the result.
+ */
+void SensorDataStoreImpl::querySum(int64_t& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end)
+{
+  std::list<SensorDataStoreReading> queryResult;
+
+  /* Issue a standard query */
+  query(queryResult, sid, start, end);
+
+  /* Integrate the result */
+  result = 0;
+
+  SensorDataStoreReading prev;
+  for (std::list<SensorDataStoreReading>::iterator it = queryResult.begin(); it != queryResult.end(); it++) {
+      if (!(it == queryResult.begin())) {
+          SensorDataStoreReading cur = *it;
+
+          /* Calculate average between two readings */
+          int64_t avg = (cur.value + prev.value) / 2;
+
+          /* Calculate time difference */
+          uint64_t dt = cur.timeStamp.getRaw() - prev.timeStamp.getRaw();
+
+          /* Sum up (with lousy attempt to keep it numerically stable - should probably use double instead) */
+          if (dt > 10000000000) {
+              /* dt > 10s => convert dt to s first */
+              dt /= 1000000000;
+              result += avg * dt;
+          }
+          else {
+              /* dt < 10s => multiply first */
+              avg *= dt;
+              result += avg / 1000000000;
+          }
+      }
+      prev = *it;
+  }
+}
+
 /**
  * @details
  * This constructor sets the internal connection variable to
@@ -284,6 +327,17 @@ void SensorDataStore::query(std::list<SensorDataStoreReading>& result, SensorId
     impl->query(result, sid, start, end);
 }
 
+/**
+ * @details
+ * Instead of doing the actual work, this function simply
+ * forwards to the insert function of the SensorDataStoreImpl
+ * class.
+ */
+void SensorDataStore::querySum(int64_t& result, SensorId sid, DCDBTimeStamp start, DCDBTimeStamp end)
+{
+    impl->querySum(result, sid, start, end);
+}
+
 /**
  * @details
  * This constructor allocates the implementation class which