Abstract over the way eventlogs are flushed

Currently eventlog data is always written to a file `progname.eventlog`.
This patch introduces the `flushEventLog` field in `RtsConfig` which
allows to customize the writing of eventlog data.

One possible scenario is the ongoing live-profile-monitor effort by
@NCrashed which slurps all eventlog data through `fluchEventLog`.

`flushEventLog` takes a buffer with eventlog data and its size and
returns `false` (0) in case eventlog data could not be procesed.

Reviewers: simonmar, austin, erikd, bgamari

Reviewed By: simonmar, bgamari

Subscribers: qnikst, thomie, NCrashed

Differential Revision: https://phabricator.haskell.org/D2934

2 files changed, 44 insertions, 0 deletions

diff --git a/includes/RtsAPI.h b/includes/RtsAPI.h
index bf25c011fc..e5326f759b 100644
--- a/includes/RtsAPI.h
+++ b/includes/RtsAPI.h
@@ -18,6 +18,7 @@ extern "C" {
 
 #include "HsFFI.h"
 #include "rts/Time.h"
+#include "rts/EventLogWriter.h"
 
 /*
  * Running the scheduler
@@ -79,6 +80,9 @@ typedef struct {
     // Whether to retain CAFs (default: false)
     HsBool keep_cafs;
 
+    // Writer a for eventlog.
+    const EventLogWriter *eventlog_writer;
+
     // Called before processing command-line flags, so that default
     // settings for RtsFlags can be provided.
     void (* defaultsHook) (void);
diff --git a/includes/rts/EventLogWriter.h b/includes/rts/EventLogWriter.h
new file mode 100644
index 0000000000..f9cb25fe62
--- /dev/null
+++ b/includes/rts/EventLogWriter.h
@@ -0,0 +1,40 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2008-2017
+ *
+ * Support for fast binary event logging.
+ *
+ * ---------------------------------------------------------------------------*/
+
+#ifndef EVENTLOG_WRITER_H
+#define EVENTLOG_WRITER_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+#include "Rts.h"
+
+/*
+ *  Abstraction for writing eventlog data.
+ */
+typedef struct {
+    // Initialize an EventLogWriter (may be NULL)
+    void (* initEventLogWriter) (void);
+
+    // Write a series of events
+    bool (* writeEventLog) (void *eventlog, size_t eventlog_size);
+
+    // Flush possibly existing buffers (may be NULL)
+    void (* flushEventLog) (void);
+
+    // Close an initialized EventLogOutput (may be NULL)
+    void (* stopEventLogWriter) (void);
+} EventLogWriter;
+
+/*
+ * An EventLogWriter which writes eventlogs to
+ * a file `program.eventlog`.
+ */
+extern const EventLogWriter FileEventLogWriter;
+
+#endif /* EVENTLOG_WRITER_H */