Add a trivial deadlock example

tests/Makefile.am

@@ -418,6 +418,7 @@ endif
 endif
 
 examplebin_PROGRAMS = \
+	main/deadlock				\
 	microbenchs/async_tasks_overhead	\
 	microbenchs/sync_tasks_overhead		\
 	microbenchs/tasks_overhead		\

tests/main/deadlock.c

@@ -0,0 +1,71 @@
+/* StarPU --- Runtime system for heterogeneous multicore architectures.
+ *
+ * Copyright (C) 2010-2021  Université de Bordeaux, CNRS (LaBRI UMR 5800), Inria
+ *
+ * StarPU is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ *
+ * StarPU 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 Lesser General Public License in COPYING.LGPL for more details.
+ */
+
+#include <starpu.h>
+#include "../helper.h"
+
+/*
+ * Create a cycle of tasks with NULL codelet, using manual dependencies.
+ * This is meant to try debugging tools with such a deadlock case.
+ */
+
+#define N	4
+
+int main(int argc, char **argv)
+{
+	int i, ret;
+
+	ret = starpu_initialize(NULL, &argc, &argv);
+	if (ret == -ENODEV) return STARPU_TEST_SKIPPED;
+	STARPU_CHECK_RETURN_VALUE(ret, "starpu_init");
+
+	struct starpu_task **tasks = (struct starpu_task **) malloc(N*sizeof(struct starpu_task *));
+
+	for (i = 0; i < N; i++)
+	{
+		tasks[i] = starpu_task_create();
+		tasks[i]->cl = NULL;
+	}
+
+	for (i = 0; i < N; i++)
+	{
+		if (i > 0)
+			starpu_task_declare_deps_array(tasks[i], 1, &tasks[i-1]);
+		else
+			starpu_task_declare_deps_array(tasks[i], 1, &tasks[N-1]);
+	}
+
+	for (i = 0; i < N; i++)
+	{
+		ret = starpu_task_submit(tasks[i]);
+		if (ret == -ENODEV) goto enodev;
+		STARPU_CHECK_RETURN_VALUE(ret, "starpu_task_submit");
+	}
+
+	starpu_task_wait_for_all();
+
+	starpu_shutdown();
+	free(tasks);
+
+	return EXIT_SUCCESS;
+
+enodev:
+	fprintf(stderr, "WARNING: No one can execute this task\n");
+	/* yes, we do not perform the computation but we did detect that no one
+ 	 * could perform the kernel, so this is not an error from StarPU */
+	starpu_shutdown();
+	return STARPU_TEST_SKIPPED;
+}