Merge concurrent lookup API requests. (#858)

Used to speedup the cold start, when multiple clients concurrently
tries to download the services URLs.
The callers are blocked until the first caller downloads the content.

Updated API lookup tests to google coding style.

Relates-To: OLPEDGE-1986

Signed-off-by: Mykhailo Kuchma <ext-mykhailo.kuchma@here.com>

Author: mykhailo-kuchma

olp-cpp-sdk-dataservice-read/src/ApiClientLookup.cpp

@@ -32,6 +32,8 @@
 #include "generated/api/ResourcesApi.h"
 #include "repositories/ApiCacheRepository.h"
 
+#include "repositories/NamedMutex.h"
+
 namespace olp {
 namespace dataservice {
 namespace read {
@@ -58,6 +60,16 @@ ApiClientLookup::ApiClientResponse ApiClientLookup::LookupApi(
     client::CancellationContext cancellation_context, std::string service,
     std::string service_version, FetchOptions options,
     client::OlpClientSettings settings) {
+
+  // This mutex is required to avoid concurrent requests to online.
+  repository::NamedMutex mutex(catalog.ToString());
+  std::unique_lock<repository::NamedMutex> lock(mutex, std::adopt_lock);
+
+  // If we are not planning to go online or access the cache, release the lock.
+  if (options != CacheOnly || options != OnlineOnly) {
+    mutex.lock();
+  }
+
   repository::ApiCacheRepository repository(catalog, settings.cache);
   const auto hrn = catalog.ToCatalogHRNString();
 
@@ -137,7 +149,6 @@ ApiClientLookup::ApiClientResponse ApiClientLookup::LookupApi(
   service_client.SetSettings(settings);
   return service_client;
 }
-
 }  // namespace read
 }  // namespace dataservice
 }  // namespace olp

olp-cpp-sdk-dataservice-read/src/repositories/NamedMutex.cpp

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2020 HERE Europe B.V.
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * License-Filename: LICENSE
+ */
+
+#include "NamedMutex.h"
+
+#include <unordered_map>
+
+namespace olp {
+namespace dataservice {
+namespace read {
+namespace repository {
+
+namespace {
+
+static std::mutex gMutex;
+
+struct RefCounterMutex {
+  std::mutex mutex;
+  uint32_t use_count{0};
+};
+
+static std::unordered_map<std::string, RefCounterMutex> gMutexes;
+
+std::mutex& AquireLock(const std::string& resource) {
+  std::unique_lock<std::mutex> lock(gMutex);
+  RefCounterMutex& ref_mutex = gMutexes[resource];
+  ref_mutex.use_count++;
+  return ref_mutex.mutex;
+}
+
+void ReleaseLock(const std::string& resource) {
+  std::unique_lock<std::mutex> lock(gMutex);
+  RefCounterMutex& ref_mutex = gMutexes[resource];
+  if (--ref_mutex.use_count == 0) {
+    gMutexes.erase(resource);
+  }
+}
+
+}  // namespace
+
+NamedMutex::NamedMutex(const std::string& name)
+    : name_{name}, mutex_{AquireLock(name_)} {}
+
+NamedMutex::~NamedMutex() { ReleaseLock(name_); }
+
+void NamedMutex::lock() { mutex_.lock(); }
+
+bool NamedMutex::try_lock() { return mutex_.try_lock(); }
+
+void NamedMutex::unlock() { mutex_.unlock(); }
+
+}  // namespace repository
+}  // namespace read
+}  // namespace dataservice
+}  // namespace olp

olp-cpp-sdk-dataservice-read/src/repositories/NamedMutex.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2020 HERE Europe B.V.
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * License-Filename: LICENSE
+ */
+
+#pragma once
+
+#include <mutex>
+#include <string>
+
+namespace olp {
+namespace dataservice {
+namespace read {
+namespace repository {
+
+/*
+ * @brief A synchronization primitive that can be used to protect shared data
+ * from being simultaneously accessed by multiple threads.
+ */
+class NamedMutex final {
+ public:
+  explicit NamedMutex(const std::string& name);
+
+  NamedMutex(const NamedMutex&) = delete;
+  NamedMutex(NamedMutex&&) = delete;
+  NamedMutex& operator=(const NamedMutex&) = delete;
+  NamedMutex& operator=(NamedMutex&&) = delete;
+
+  void lock();
+  bool try_lock();
+  void unlock();
+
+  ~NamedMutex();
+
+ private:
+  std::string name_;
+  std::mutex& mutex_;
+};
+
+}  // namespace repository
+}  // namespace read
+}  // namespace dataservice
+}  // namespace olp