[RFC 4/6] Introduce run_on_main_thread

Tom Tromey
2019-03-09T17:23:08Z

This introduces a way for a callback to be run on the main thread.

2019-03-08 Tom Tromey <tom@tromey.com>

* ser-event.h (run_on_main_thread): Declare.
* ser-event.c (runnable_event, runnables, runnable_mutex): New
globals.
(run_events, run_on_main_thread, _initialize_ser_event): New
functions.
---
gdb/ChangeLog | 8 +++++++
gdb/ser-event.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++
gdb/ser-event.h | 6 +++++
3 files changed, 73 insertions(+)

diff --git a/gdb/ser-event.c b/gdb/ser-event.c
index d3956346246..821b2f169df 100644
--- a/gdb/ser-event.c
+++ b/gdb/ser-event.c
@@ -20,6 +20,8 @@
#include "ser-event.h"
#include "serial.h"
#include "common/filestuff.h"
+#include <mutex>
+#include "event-loop.h"

/* On POSIX hosts, a serial_event is basically an abstraction for the
classical self-pipe trick.
@@ -217,3 +219,60 @@ serial_event_clear (struct serial_event *event)
ResetEvent (state->event);
#endif
}
+
+\f
+
+/* The serial event used when posting runnables. */
+
+static struct serial_event *runnable_event;
+
+/* Runnables that have been posted. */
+
+static std::vector<std::function<void ()>> runnables;
+
+/* Mutex to hold when handling runnable_event or runnables. */
+
+static std::mutex runnable_mutex;
+
+/* Run all the queued runnables. */
+
+static void
+run_events (int error, gdb_client_data client_data)
+{
+ std::vector<std::function<void ()>> local;
+
+ /* Hold the lock while changing the globals, but not while running
+ the runnables. */
+ {
+ std::lock_guard<std::mutex> lock (runnable_mutex);
+
+ /* Clear the event fd. Do this before flushing the events list,
+ so that any new event post afterwards is sure to re-awaken the
+ event loop. */
+ serial_event_clear (runnable_event);
+
+ /* Move the vector in case running a runnable pushes a new
+ runnable. */
+ std::swap (local, runnables);
+ }
+
+ for (auto &item : local)
+ item ();
+}
+
+/* See ser-event.h. */
+
+void
+run_on_main_thread (std::function<void ()> &&func)
+{
+ std::lock_guard<std::mutex> lock (runnable_mutex);
+ runnables.emplace_back (std::move (func));
+ serial_event_set (runnable_event);
+}
+
+void
+_initialize_ser_event ()
+{
+ runnable_event = make_serial_event ();
+ add_file_handler (serial_event_fd (runnable_event), run_events, nullptr);
+}
diff --git a/gdb/ser-event.h b/gdb/ser-event.h
index 137348557f9..61a84f9cc79 100644
--- a/gdb/ser-event.h
+++ b/gdb/ser-event.h
@@ -19,6 +19,8 @@
#ifndef SER_EVENT_H
#define SER_EVENT_H

+#include <functional>
+
/* This is used to be able to signal the event loop (or any other
select/poll) of events, in a race-free manner.

@@ -48,4 +50,8 @@ extern void serial_event_set (struct serial_event *event);
call is made. */
extern void serial_event_clear (struct serial_event *event);

+/* Send a runnable to the main thread. */
+
+extern void run_on_main_thread (std::function<void ()> &&);
+
#endif
--
2.17.2