core: Add global threading utility

For now, we only store what's the main thread of the program.

src/core/gcal-core-macros.h

@@ -0,0 +1,31 @@
+/*
+ * gcal-core-macros.h
+ *
+ * Copyright 2023 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
+ *
+ * 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/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include "gcal-global.h"
+
+G_BEGIN_DECLS
+
+#define GCAL_IS_THREAD(thread_) (g_thread_self () == (thread_))
+#define GCAL_IS_MAIN_THREAD() (g_thread_self () == gcal_get_main_thread ())
+
+G_END_DECLS

src/core/gcal-global.c

@@ -0,0 +1,47 @@
+/*
+ * gcal-global.c
+ *
+ * Copyright 2023 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
+ *
+ * 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/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include "gcal-global.h"
+#include "gconstructor.h"
+
+static GThread *main_thread;
+
+#if defined (G_HAS_CONSTRUCTORS)
+# ifdef G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA
+#  pragma G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(gcal_init_ctor)
+# endif
+G_DEFINE_CONSTRUCTOR(gcal_init_ctor)
+#else
+# error Your platform/compiler is missing constructor support
+#endif
+
+static void
+gcal_init_ctor (void)
+{
+  main_thread = g_thread_self ();
+}
+
+GThread *
+gcal_get_main_thread (void)
+{
+  return main_thread;
+}
+

src/core/gcal-global.h

@@ -0,0 +1,30 @@
+/*
+ * gcal-global.h
+ *
+ * Copyright 2023 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
+ *
+ * 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/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+GThread *            gcal_get_main_thread                        (void);
+
+G_END_DECLS

src/core/meson.build

@@ -6,6 +6,7 @@ sources += files(
   'gcal-clock.c',
   'gcal-context.c',
   'gcal-event.c',
+  'gcal-global.c',
   'gcal-log.c',
   'gcal-manager.c',
   'gcal-range.c',