[libc] Add a linux Thread class in __support/threads.

This change is essentially a mechanical change which moves the thread
creation and join implementations from src/threads/linux to
src/__support/threads/linux/thread.h. The idea being that, in future, a
pthread implementation can reuse the common thread implementations in
src/__support/threads.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D123287

1 files changed, 30 insertions, 0 deletions

diff --git a/libc/src/threads/thrd_join.cpp b/libc/src/threads/thrd_join.cpp
new file mode 100644
index 000000000000..20096a7be1bf
--- /dev/null
+++ b/libc/src/threads/thrd_join.cpp
@@ -0,0 +1,30 @@
+//===-- Linux implementation of the thrd_join function --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/threads/thrd_join.h"
+#include "src/__support/common.h"
+#include "src/__support/threads/thread.h"
+
+#include <threads.h> // For thrd_* type definitions.
+
+namespace __llvm_libc {
+
+static_assert(sizeof(thrd_t) == sizeof(__llvm_libc::Thread<int>),
+              "Mismatch between thrd_t and internal Thread<int>.");
+
+LLVM_LIBC_FUNCTION(int, thrd_join, (thrd_t * th, int *retval)) {
+  auto *thread = reinterpret_cast<Thread<int> *>(th);
+  int result = thread->join();
+  if (result == 0) {
+    *retval = thread->return_value();
+    return thrd_success;
+  }
+  return thrd_error;
+}
+
+} // namespace __llvm_libc