Releasing the former Stadia file transfer tools

The tools allow efficient and fast synchronization of large directory
trees from a Windows workstation to a Linux target machine.

cdc_rsync* support efficient copy of files by using content-defined
chunking (CDC) to identify chunks within files that can be reused.

asset_stream_manager + cdc_fuse_fs support efficient streaming of a
local directory to a remote virtual file system based on FUSE. It also
employs CDC to identify and reuse unchanged data chunks.

common/semaphore_test.cc

@@ -0,0 +1,122 @@
+// Copyright 2022 Google LLC
+//
+// 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 "common/semaphore.h"
+
+#include <atomic>
+#include <thread>
+#include <vector>
+
+#include "common/util.h"
+#include "gtest/gtest.h"
+
+namespace cdc_ft {
+namespace {
+
+class SemaphoreTest : public ::testing::Test {
+ protected:
+  bool PollUntil(std::function<bool()> predicate, uint32_t timeout_ms) {
+    uint32_t ms = 0;
+    while (!predicate()) {
+      Util::Sleep(1);
+
+      ms++;
+      if (ms >= timeout_ms) {
+        return false;
+      }
+    }
+    return true;
+  }
+};
+
+TEST_F(SemaphoreTest, BlocksIfInitialCountIsZero) {
+  Semaphore semaphore(0);
+  std::atomic_bool ready(false);
+  std::atomic_bool done(false);
+  std::thread thread([&semaphore, &ready, &done]() {
+    ready = true;
+    semaphore.Wait();
+    done = true;
+  });
+  EXPECT_TRUE(PollUntil([&ready]() { return ready.load(); }, 5000));
+  // This will time out, so use a short timeout. Is there a way to test whether
+  // the thread is blocking without using a timeout?
+  EXPECT_FALSE(PollUntil([&done]() { return done.load(); }, 10));
+  semaphore.Signal();
+  EXPECT_TRUE(PollUntil([&done]() { return done.load(); }, 5000));
+  thread.join();
+}
+
+TEST_F(SemaphoreTest, DoesNotBlockIfInitialCountIsOne) {
+  Semaphore semaphore(1);
+  std::atomic_bool first_wait(false);
+  std::atomic_bool done(false);
+  std::thread thread([&semaphore, &first_wait, &done]() {
+    semaphore.Wait();
+    first_wait = true;
+    semaphore.Wait();
+    done = true;
+  });
+  EXPECT_TRUE(PollUntil([&first_wait]() { return first_wait.load(); }, 5000));
+  // This will time out, so use a short timeout. Is there a way to test whether
+  // the thread is blocking without using a timeout?
+  EXPECT_FALSE(PollUntil([&done]() { return done.load(); }, 10));
+  semaphore.Signal();
+  EXPECT_TRUE(PollUntil([&done]() { return done.load(); }, 5000));
+  thread.join();
+}
+
+TEST_F(SemaphoreTest, SignalManyThreads) {
+  Semaphore semaphore(0);
+  std::atomic_int a(0);
+  std::atomic_int b(0);
+  std::atomic_int c(0);
+
+  const int N = 16;
+  std::vector<std::thread> threads;
+  for (int n = 0; n < N; ++n) {
+    threads.emplace_back([&semaphore, &a, &b, &c]() {
+      ++a;
+      semaphore.Wait();
+      ++b;
+      semaphore.Wait();
+      ++c;
+    });
+  }
+
+  // All threads should be at the first wait.
+  EXPECT_TRUE(PollUntil([&]() { return a == N; }, 5000));
+
+  for (int n = 0; n < N; ++n) {
+    semaphore.Signal();
+  }
+
+  // Some threads should be at or past the second wait.
+  // Note: If the Semaphore were fair, it would be cnt[1] == N and cnt[2] == 0.
+  EXPECT_TRUE(PollUntil([&]() { return b + c == N; }, 5000));
+
+  for (int n = 0; n < N; ++n) {
+    semaphore.Signal();
+  }
+
+  // All threads should have finished.
+  EXPECT_TRUE(PollUntil([&]() { return b == N && c == N; }, 5000));
+
+  for (int n = 0; n < N; ++n) {
+    threads[n].join();
+  }
+}
+
+}  // namespace
+}  // namespace cdc_ft