threads: introduce `git_thread_exit`

Introduce `git_thread_exit`, which will allow threads to terminate at an
arbitrary time, returning a `void *`.  On Windows, this means that we
need to store the current `git_thread` in TLS, so that we can set its
`return` value when terminating.

We cannot simply use `ExitThread`, since Win32 returns `DWORD`s from
threads; we return `void *`.

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/threads/basic.c b/tests/threads/basic.c
index 9c342bc42..685452d44 100644
--- a/tests/threads/basic.c
+++ b/tests/threads/basic.c
@@ -48,3 +48,30 @@ void test_threads_basic__set_error(void)
 {
 	run_in_parallel(1, 4, set_error, NULL, NULL);
 }
+
+static void *return_normally(void *param)
+{
+	return param;
+}
+
+static void *exit_abruptly(void *param)
+{
+	git_thread_exit(param);
+	return NULL;
+}
+
+void test_threads_basic__exit(void)
+{
+	git_thread thread;
+	void *result;
+
+	/* Ensure that the return value of the threadproc is returned. */
+	cl_git_pass(git_thread_create(&thread, return_normally, (void *)424242));
+	cl_git_pass(git_thread_join(&thread, &result));
+	cl_assert_equal_sz(424242, (size_t)result);
+
+	/* Ensure that the return value of `git_thread_exit` is returned. */
+	cl_git_pass(git_thread_create(&thread, return_normally, (void *)232323));
+	cl_git_pass(git_thread_join(&thread, &result));
+	cl_assert_equal_sz(232323, (size_t)result);
+}
\ No newline at end of file