[tor-commits] [tor/master] Add a mechanism for the logging system to report queued callbacks

[nickm at torproject.org]

commit b0224bf7282f2ec968a46e35a2a8dab1ddaf0667
Author: Nick Mathewson <nickm at torproject.org>
Date:   Tue May 1 10:05:22 2018 -0400

    Add a mechanism for the logging system to report queued callbacks
    
    Sometimes the logging system will queue a log message for later.
    When it does this, the callback will either get flushed at the next
    safe time, or from the second-elapsed callback.
    
    But we're trying to eliminate the second-elapsed callback, so let's
    make a way for the log system to tell its users about this.
---
 src/common/log.c    | 25 +++++++++++++++++++++++++
 src/common/torlog.h |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/src/common/log.c b/src/common/log.c
index 922e9dd38..ebd50f62d 100644
--- a/src/common/log.c
+++ b/src/common/log.c
@@ -170,6 +170,9 @@ typedef struct pending_log_message_t {
 /** Log messages waiting to be replayed onto callback-based logs */
 static smartlist_t *pending_cb_messages = NULL;
 
+/** Callback to invoke when pending_cb_messages becomes nonempty. */
+static pending_callback_callback pending_cb_cb = NULL;
+
 /** Log messages waiting to be replayed once the logging system is initialized.
  */
 static smartlist_t *pending_startup_messages = NULL;
@@ -538,6 +541,9 @@ logfile_deliver(logfile_t *lf, const char *buf, size_t msg_len,
         smartlist_add(pending_cb_messages,
             pending_log_message_new(severity,domain,NULL,msg_after_prefix));
         *callbacks_deferred = 1;
+        if (smartlist_len(pending_cb_messages) == 1 && pending_cb_cb) {
+          pending_cb_cb();
+        }
       }
     } else {
       lf->callback(severity, domain, msg_after_prefix);
@@ -825,6 +831,7 @@ logs_free_all(void)
   logfiles = NULL;
   messages = pending_cb_messages;
   pending_cb_messages = NULL;
+  pending_cb_cb = NULL;
   messages2 = pending_startup_messages;
   pending_startup_messages = NULL;
   UNLOCK_LOGS();
@@ -988,6 +995,24 @@ add_temp_log(int min_severity)
 }
 
 /**
+ * Register "cb" as the callback to call when there are new pending log
+ * callbacks to be flushed with flush_pending_log_callbacks().
+ *
+ * Note that this callback, if present, can be invoked from any thread.
+ *
+ * This callback must not log.
+ *
+ * It is intentional that this function contains the name "callback" twice: it
+ * sets a "callback" to be called on the condition that there is a "pending
+ * callback".
+ **/
+void
+logs_set_pending_callback_callback(pending_callback_callback cb)
+{
+  pending_cb_cb = cb;
+}
+
+/**
  * Add a log handler to send messages in <b>severity</b>
  * to the function <b>cb</b>.
  */
diff --git a/src/common/torlog.h b/src/common/torlog.h
index ac632ff52..de389883c 100644
--- a/src/common/torlog.h
+++ b/src/common/torlog.h
@@ -154,6 +154,8 @@ int add_android_log(const log_severity_list_t *severity,
                     const char *android_identity_tag);
 #endif // HAVE_ANDROID_LOG_H.
 int add_callback_log(const log_severity_list_t *severity, log_callback cb);
+typedef void (*pending_callback_callback)(void);
+void logs_set_pending_callback_callback(pending_callback_callback cb);
 void logs_set_domain_logging(int enabled);
 int get_min_log_level(void);
 void switch_logs_debug(void);