Move thread_util to libnetdutils

This change comprises:

[1] Move thread_util.h to libnetdutils to ease the cleanup of the
    include path system/netd/server for libnetd_resolv.

[2] Rename thread_util.h to ThreadUtil.h.

[3] Add the test to ThreadUtilTest.

Bug: 128662167
Test: system/netd/tests/runtests.sh passed
Change-Id: Ia8e9b196fbe41a4bd1edc7592badaacf57165988
diff --git a/libnetdutils/include/netdutils/ThreadUtil.h b/libnetdutils/include/netdutils/ThreadUtil.h
new file mode 100644
index 0000000..2ef97ef
--- /dev/null
+++ b/libnetdutils/include/netdutils/ThreadUtil.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef NETDUTILS_THREADUTIL_H
+#define NETDUTILS_THREADUTIL_H
+
+#include <pthread.h>
+#include <memory>
+
+#include <android-base/logging.h>
+
+namespace android {
+namespace netdutils {
+
+struct scoped_pthread_attr {
+    scoped_pthread_attr() { pthread_attr_init(&attr); }
+    ~scoped_pthread_attr() { pthread_attr_destroy(&attr); }
+
+    int detach() { return -pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); }
+
+    pthread_attr_t attr;
+};
+
+template <typename T>
+inline void* runAndDelete(void* obj) {
+    std::unique_ptr<T> handler(reinterpret_cast<T*>(obj));
+    handler->run();
+    return nullptr;
+}
+
+template <typename T>
+inline int threadLaunch(T* obj) {
+    if (obj == nullptr) {
+        return -EINVAL;
+    }
+
+    scoped_pthread_attr scoped_attr;
+
+    int rval = scoped_attr.detach();
+    if (rval != 0) {
+        return rval;
+    }
+
+    pthread_t thread;
+    rval = pthread_create(&thread, &scoped_attr.attr, &runAndDelete<T>, obj);
+    if (rval != 0) {
+        LOG(WARNING) << __func__ << ": pthread_create failed: " << rval;
+        return -rval;
+    }
+
+    return rval;
+}
+
+}  // namespace netdutils
+}  // namespace android
+
+#endif  // NETDUTILS_THREADUTIL_H