[PATCH v4 07/11] Introduce run_on_main_thread

Tom Tromey
2019-10-01T20:12:42Z

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

gdb/ChangeLog
2019-10-01 Tom Tromey <tom@tromey.com>

* unittests/main-thread-selftests.c: New file.
* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add
main-thread-selftests.c.
* 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 | 11 ++++
gdb/Makefile.in | 1 +
gdb/ser-event.c | 78 ++++++++++++++++++++++++++
gdb/ser-event.h | 6 ++
gdb/unittests/main-thread-selftests.c | 80 +++++++++++++++++++++++++++
5 files changed, 176 insertions(+)
create mode 100644 gdb/unittests/main-thread-selftests.c

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index c4c858b5594..d4eca61d06e 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -426,6 +426,7 @@ SUBDIR_UNITTESTS_SRCS = \
unittests/optional-selftests.c \
unittests/parse-connection-spec-selftests.c \
unittests/ptid-selftests.c \
+ unittests/main-thread-selftests.c \
unittests/mkdir-recursive-selftests.c \
unittests/rsp-low-selftests.c \
unittests/scoped_fd-selftests.c \
diff --git a/gdb/ser-event.c b/gdb/ser-event.c
index a65a186526f..029ced7619c 100644
--- a/gdb/ser-event.c
+++ b/gdb/ser-event.c
@@ -20,6 +20,10 @@
#include "ser-event.h"
#include "serial.h"
#include "gdbsupport/filestuff.h"
+#if CXX_STD_THREAD
+#include <mutex>
+#endif
+#include "event-loop.h"

/* On POSIX hosts, a serial_event is basically an abstraction for the
classical self-pipe trick.
@@ -217,3 +221,77 @@ 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;
+
+#if CXX_STD_THREAD
+
+/* Mutex to hold when handling runnable_event or runnables. */
+
+static std::mutex runnable_mutex;
+
+#endif
+
+/* 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. */
+ {
+#if CXX_STD_THREAD
+ std::lock_guard<std::mutex> lock (runnable_mutex);
+#endif
+
+ /* 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. */
+ local = std::move (runnables);
+ }
+
+ for (auto &item : local)
+ {
+ try
+ {
+ item ();
+ }
+ catch (...)
+ {
+ /* Ignore exceptions in the callback. */
+ }
+ }
+}
+
+/* See ser-event.h. */
+
+void
+run_on_main_thread (std::function<void ()> &&func)
+{
+#if CXX_STD_THREAD
+ std::lock_guard<std::mutex> lock (runnable_mutex);
+#endif
+ 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
diff --git a/gdb/unittests/main-thread-selftests.c b/gdb/unittests/main-thread-selftests.c
new file mode 100644
index 00000000000..e5bd2d36cea
--- /dev/null
+++ b/gdb/unittests/main-thread-selftests.c
@@ -0,0 +1,80 @@
+/* Self tests for run_on_main_thread
+
+ Copyright (C) 2019 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "defs.h"
+#include "gdbsupport/selftest.h"
+#include "gdbsupport/block-signals.h"
+#include "ser-event.h"
+#include "event-loop.h"
+#if CXX_STD_THREAD
+#include <thread>
+#endif
+
+namespace selftests {
+namespace main_thread_tests {
+
+#if CXX_STD_THREAD
+
+static bool done;
+
+static void
+set_done ()
+{
+ run_on_main_thread ([] ()
+ {
+ done = true;
+ });
+}
+
+static void
+run_tests ()
+{
+ std::thread thread;
+
+ done = false;
+
+ {
+ gdb::block_signals blocker;
+
+ thread = std::thread (set_done);
+ }
+
+ while (!done && gdb_do_one_event () >= 0)
+ ;
+
+ /* Actually the test will just hang, but we want to test
+ something. */
+ SELF_CHECK (done);
+
+ thread.join ();
+}
+
+#endif
+
+}
+}
+
+void
+_initialize_main_thread_selftests ()
+{
+#if CXX_STD_THREAD
+ selftests::register_test ("main_thread",
+ selftests::main_thread_tests::run_tests);
+#endif
+}
--
2.17.2