[#235] Wrap pgagroal_prefill()

In order to make calls to `pgagroal_prefill()` consistent around the
code and avoid repetitions, there is a new function named
`pgagroal_prefill_if_can()` that wraps several checks and does the
forking and prefilling.
Therefore there is no need to check against the configuration limits
and users before calling `pgagroal_prefill()` because
`pgagroal_prefill_if_can()` will do by itself.

Also `pgagroal_prefill_if_can()` will check for a primary server, and
in the case there is none, will avoid issuing the prefill at all.

Last, this introduces also the `pgagroal_can_prefill()` function that
is used in turn by `pgagroal_prefill_if_can()` and aims at testing the
configuration for the presence of limits and users. This function can
be used as a condition checker before doing clean-up stuff right
before calling `pgagroal_prefill_if_can()`.

Close #223

src/include/configuration.h

@@ -182,6 +182,17 @@ pgagroal_reload_configuration(void);
 void
 pgagroal_init_pidfile_if_needed(struct configuration* config);
 
+/**
+ * Checks if the configuration has a min set of values to
+ * take into account doing a prefill. For example, there must
+ * be users and limits set, otherwise it does not
+ * make any sense to attempt a prefill.
+ * This can be used to wrap the condituion before calling
+ * other prefill functions, e.g., `pgagroal_prefill()`.
+ */
+bool
+pgagroal_can_prefill(void);
+
 #ifdef __cplusplus
 }
 #endif

src/include/pool.h

@@ -126,6 +126,24 @@ pgagroal_pool_shutdown(void);
 int
 pgagroal_pool_status(void);
 
+/**
+ * This function wraps around the logic to call `pgagroal_prefill()`.
+ * In order to avoid code repetition, this function can be used safely
+ * wherever there is the possibility to activate the prefill. The function
+ * does check if the configuration allows for a prefill, and in such case
+ * tries to `fork(2)` and executes the prefill.
+ * Also, the function checks for the presence of a primary with
+ * `pgagroal_get_primary()` and refuses to do a prefill if there
+ * is no primary at all.
+ *
+ * @param initial true if the prefill has to be done with the INITIAL
+ *        value of the pgagroal_database.conf file, false if it has
+ *        to be done with the MINIMAL value.
+ *
+ */
+void
+pgagroal_prefill_if_can(bool initial);
+
 #ifdef __cplusplus
 }
 #endif

src/libpgagroal/configuration.c

@@ -3169,3 +3169,20 @@ pgagroal_init_pidfile_if_needed(struct configuration* config)
       pgagroal_log_debug("PID file automatically set to: [%s]", config->pidfile);
    }
 }
+
+bool
+pgagroal_can_prefill(void)
+{
+   struct configuration* config;
+
+   config = (struct configuration*)shmem;
+
+   if (config->number_of_users > 0 && config->number_of_limits > 0)
+   {
+      return true;
+   }
+   else
+   {
+      return false;
+   }
+}

src/libpgagroal/pool.c

@@ -39,6 +39,7 @@
 #include <server.h>
 #include <tracker.h>
 #include <utils.h>
+#include <configuration.h>
 
 /* system */
 #include <assert.h>
@@ -252,13 +253,7 @@ pgagroal_get_connection(char* username, char* database, bool reuse, bool transac
             pgagroal_tracking_event_slot(TRACKER_BAD_CONNECTION, *slot);
             status = pgagroal_kill_connection(*slot, *ssl);
 
-            if (config->number_of_users > 0 && config->number_of_limits > 0)
-            {
-               if (!fork())
-               {
-                  pgagroal_prefill(false);
-               }
-            }
+            pgagroal_prefill_if_can(false);
 
             if (status == 0)
             {
@@ -577,12 +572,9 @@ pgagroal_idle_timeout(void)
       }
    }
 
-   if (prefill && config->number_of_users > 0 && config->number_of_limits > 0)
+   if (prefill)
    {
-      if (!fork())
-      {
-         pgagroal_prefill(false);
-      }
+      pgagroal_prefill_if_can(false);
    }
 
    pgagroal_pool_status();
@@ -662,12 +654,9 @@ pgagroal_validation(void)
       }
    }
 
-   if (prefill && config->number_of_users > 0 && config->number_of_limits > 0)
+   if (prefill)
    {
-      if (!fork())
-      {
-         pgagroal_prefill(false);
-      }
+      pgagroal_prefill_if_can(false);
    }
 
    pgagroal_pool_status();
@@ -783,12 +772,9 @@ pgagroal_flush(int mode, char* database)
       }
    }
 
-   if (prefill && config->number_of_users > 0 && config->number_of_limits > 0)
+   if (prefill)
    {
-      if (!fork())
-      {
-         pgagroal_prefill(false);
-      }
+      pgagroal_prefill_if_can(false);
    }
 
    pgagroal_pool_status();
@@ -852,12 +838,9 @@ pgagroal_flush_server(signed char server)
    }
    else
    {
-      if (config->number_of_users > 0 && config->number_of_limits > 0 && server != (unsigned char)primary && primary != -1)
+      if (server != (unsigned char)primary && primary != -1)
       {
-         if (!fork())
-         {
-            pgagroal_prefill(true);
-         }
+         pgagroal_prefill_if_can(true);
       }
    }
 
@@ -1359,3 +1342,23 @@ do_prefill(char* username, char* database, int size)
 
    return connections < size && free > 0;
 }
+
+void
+pgagroal_prefill_if_can(bool initial)
+{
+   int primary;
+
+   if (pgagroal_can_prefill())
+   {
+      if (pgagroal_get_primary(&primary))
+      {
+         pgagroal_log_warn("No primary detected, cannot try to prefill!");
+         return;
+      }
+
+      if (!fork())
+      {
+         pgagroal_prefill(initial);
+      }
+   }
+}

src/main.c

@@ -1060,12 +1060,12 @@ main(int argc, char** argv)
       pgagroal_log_warn("No users allowed");
    }
 
-   if (config->number_of_users > 0)
+   if (pgagroal_can_prefill())
    {
       if (!fork())
       {
          shutdown_ports();
-         pgagroal_prefill(true);
+         pgagroal_prefill_if_can(true);
       }
    }