perl plugin: Fix a race condition.

This hopefully fixes GitHub issue #9.

diff --git a/src/perl.c b/src/perl.c
index a2f5da2..41e763d 100644 (file)
--- a/src/perl.c
+++ b/src/perl.c
@@ -1923,6 +1923,11 @@ static int perl_read (void)
                aTHX = t->interp;
        }
 
+       /* Assert that we're not running as the base thread. Otherwise, we might
+        * run into concurrency issues with c_ithread_create(). See
+        * https://github.com/collectd/collectd/issues/9 for details. */
+       assert (aTHX != perl_threads->head->interp);
+
        log_debug ("perl_read: c_ithread: interp = %p (active threads: %i)",
                        aTHX, perl_threads->number_of_threads);
        return pplugin_call_all (aTHX_ PLUGIN_READ);
@@ -1931,6 +1936,7 @@ static int perl_read (void)
 static int perl_write (const data_set_t *ds, const value_list_t *vl,
                user_data_t __attribute__((unused)) *user_data)
 {
+       int status;
        dTHX;
 
        if (NULL == perl_threads)
@@ -1946,9 +1952,20 @@ static int perl_write (const data_set_t *ds, const value_list_t *vl,
                aTHX = t->interp;
        }
 
+       /* Lock the base thread if this is not called from one of the read threads
+        * to avoid race conditions with c_ithread_create(). See
+        * https://github.com/collectd/collectd/issues/9 for details. */
+       if (aTHX == perl_threads->head->interp)
+               pthread_mutex_lock (&perl_threads->mutex);
+
        log_debug ("perl_write: c_ithread: interp = %p (active threads: %i)",
                        aTHX, perl_threads->number_of_threads);
-       return pplugin_call_all (aTHX_ PLUGIN_WRITE, ds, vl);
+       status = pplugin_call_all (aTHX_ PLUGIN_WRITE, ds, vl);
+
+       if (aTHX == perl_threads->head->interp)
+               pthread_mutex_unlock (&perl_threads->mutex);
+
+       return status;
 } /* static int perl_write (const data_set_t *, const value_list_t *) */
 
 static void perl_log (int level, const char *msg,
@@ -1969,7 +1986,17 @@ static void perl_log (int level, const char *msg,
                aTHX = t->interp;
        }
 
+       /* Lock the base thread if this is not called from one of the read threads
+        * to avoid race conditions with c_ithread_create(). See
+        * https://github.com/collectd/collectd/issues/9 for details. */
+       if (aTHX == perl_threads->head->interp)
+               pthread_mutex_lock (&perl_threads->mutex);
+
        pplugin_call_all (aTHX_ PLUGIN_LOG, level, msg);
+
+       if (aTHX == perl_threads->head->interp)
+               pthread_mutex_unlock (&perl_threads->mutex);
+
        return;
 } /* static void perl_log (int, const char *) */