[PATCH v6 1/2] selftests/futex: implement the interfaces related to threads

[Yuwen Chen <ywen.chen@foxmail.com>]

There are timing issues in the use of threads in some unit test cases
for futex. A potentially good solution is to check whether the thread
is in the sleep state after creating it.

A file named futex_thread.h is added, in which several thread-related
functions are implemented to facilitate the solution of this problem.

Signed-off-by: Yuwen Chen <ywen.chen@foxmail.com>
---
 .../selftests/futex/include/futex_thread.h    | 109 ++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 tools/testing/selftests/futex/include/futex_thread.h

diff --git a/tools/testing/selftests/futex/include/futex_thread.h b/tools/testing/selftests/futex/include/futex_thread.h
new file mode 100644
index 0000000000000..7520ea8e8f885
--- /dev/null
+++ b/tools/testing/selftests/futex/include/futex_thread.h
@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _FUTEX_THREAD_H
+#define _FUTEX_THREAD_H
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#define USEC_PER_SEC 1000000L
+#define WAIT_THREAD_RETRIES 100
+
+struct futex_thread {
+	pthread_t		thread;
+	pthread_barrier_t	barrier;
+	pid_t			tid;
+	int			(*threadfn)(void *arg);
+	void			*arg;
+	int			retval;
+};
+
+static int __wait_for_thread(FILE *fp, int timeout_us)
+{
+	char buf[80] = "";
+	int i;
+
+	for (i = 0; i < WAIT_THREAD_RETRIES; i++) {
+		if (!fgets(buf, sizeof(buf), fp))
+			return -EIO;
+		if (!strncmp(buf, "futex", 5))
+			return 0;
+		usleep(timeout_us / WAIT_THREAD_RETRIES);
+		rewind(fp);
+	}
+	return -ETIMEDOUT;
+}
+
+static void *__futex_thread_fn(void *arg)
+{
+	struct futex_thread *t = arg;
+
+	t->tid = gettid();
+	pthread_barrier_wait(&t->barrier);
+	t->retval = t->threadfn(t->arg);
+	return NULL;
+}
+
+/**
+ * futex_wait_for_thread - Wait for the child thread to sleep in the futex context
+ * @t:          Thread handle.
+ * @timeout_us: The timeout for waiting for the thread to enter the sleep state.
+ */
+static int futex_wait_for_thread(struct futex_thread *t, int timeout_us)
+{
+	char fname[80];
+	FILE *fp;
+	int res;
+
+	snprintf(fname, sizeof(fname), "/proc/%d/wchan", t->tid);
+	fp = fopen(fname, "r");
+	if (!fp) {
+		usleep(USEC_PER_SEC / 10); /* 100ms */
+		return -EIO;
+	}
+
+	res = __wait_for_thread(fp, timeout_us);
+	if (res == -EIO)
+		usleep(USEC_PER_SEC / 10); /* 100ms */
+
+	fclose(fp);
+	return res;
+}
+
+/**
+ * futex_thread_create - Create a new thread for testing.
+ * @t:        The handle of the newly created thread.
+ * @threadfn: The new thread starts execution by invoking threadfn
+ * @arg:      The parameters passed to threadfn.
+ */
+static int futex_thread_create(struct futex_thread *t, int (*threadfn)(void *), void *arg)
+{
+	int ret;
+
+	pthread_barrier_init(&t->barrier, NULL, 2);
+	t->tid = 0;
+	t->threadfn = threadfn;
+	t->arg = arg;
+
+	ret = pthread_create(&t->thread, NULL, __futex_thread_fn, t);
+	if (ret)
+		return ret;
+
+	pthread_barrier_wait(&t->barrier);
+	return 0;
+}
+
+/**
+ * futex_thread_destroy - Wait for and reclaim the resources of the thread.
+ * @t:      Thread handle.
+ */
+static int futex_thread_destroy(struct futex_thread *t)
+{
+	pthread_join(t->thread, NULL);
+	pthread_barrier_destroy(&t->barrier);
+	return t->retval;
+}
+
+#endif
-- 
2.34.1