adb: sysdeps: add support for joining threads.

Bug: http://b/27105824
Change-Id: I44e4edbb2a59565c35f1f3e6a6394ac258591f95
diff --git a/adb/sysdeps_test.cpp b/adb/sysdeps_test.cpp
new file mode 100644
index 0000000..24a0d6f
--- /dev/null
+++ b/adb/sysdeps_test.cpp
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2065 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.
+ */
+
+#include <gtest/gtest.h>
+#include <unistd.h>
+#include <atomic>
+
+#include "sysdeps.h"
+
+static void* increment_atomic_int(void* c) {
+    sleep(1);
+    reinterpret_cast<std::atomic<int>*>(c)->fetch_add(1);
+    return nullptr;
+}
+
+TEST(sysdeps_thread, smoke) {
+    std::atomic<int> counter(0);
+
+    for (int i = 0; i < 100; ++i) {
+        ASSERT_TRUE(adb_thread_create(increment_atomic_int, &counter));
+    }
+
+    sleep(2);
+    ASSERT_EQ(100, counter.load());
+}
+
+TEST(sysdeps_thread, join) {
+    std::atomic<int> counter(0);
+    std::vector<adb_thread_t> threads(500);
+    for (size_t i = 0; i < threads.size(); ++i) {
+        ASSERT_TRUE(adb_thread_create(increment_atomic_int, &counter, &threads[i]));
+    }
+
+    int current = counter.load();
+    ASSERT_GE(current, 0);
+    // Make sure that adb_thread_create actually creates threads, and doesn't do something silly
+    // like synchronously run the function passed in. The sleep in increment_atomic_int should be
+    // enough to keep this from being flakey.
+    ASSERT_LT(current, 500);
+
+    for (const auto& thread : threads) {
+        ASSERT_TRUE(adb_thread_join(thread));
+    }
+
+    ASSERT_EQ(500, counter.load());
+}