chore: import upstream snapshot with attribution

test/bthread_sched_yield_unittest.cpp

@@ -0,0 +1,64 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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.
+
+#include <gtest/gtest.h>
+#include <pthread.h>
+#include <sched.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <bthread/processor.h>
+
+namespace {
+volatile bool stop = false;
+
+void* spinner(void*) {
+    long counter = 0;
+    for (; !stop; ++counter) {
+        cpu_relax();
+    }
+    printf("spinned %ld\n", counter);
+    return NULL;
+}
+
+void* yielder(void*) {
+    int counter = 0;
+    for (; !stop; ++counter) {
+        sched_yield();
+    }
+    printf("sched_yield %d\n", counter);
+    return NULL;
+}
+
+TEST(SchedYieldTest, sched_yield_when_all_core_busy) {
+    stop = false;
+    const int kNumCores = sysconf(_SC_NPROCESSORS_ONLN);
+    ASSERT_TRUE(kNumCores > 0);
+    pthread_t th0;
+    pthread_create(&th0, NULL, yielder, NULL);
+    
+    pthread_t th[kNumCores];
+    for (int i = 0; i < kNumCores; ++i) {
+        pthread_create(&th[i], NULL, spinner, NULL);
+    }
+    sleep(1);
+    stop = true;
+    for (int i = 0; i < kNumCores; ++i) {
+        pthread_join(th[i], NULL);
+    }
+    pthread_join(th0, NULL);
+}
+} // namespace