diff --git a/automotive/vehicle/aidl/impl/fake_impl/hardware/test/FakeVehicleHardwareTest.cpp b/automotive/vehicle/aidl/impl/fake_impl/hardware/test/FakeVehicleHardwareTest.cpp
index f8df6e6..970d044 100644
--- a/automotive/vehicle/aidl/impl/fake_impl/hardware/test/FakeVehicleHardwareTest.cpp
+++ b/automotive/vehicle/aidl/impl/fake_impl/hardware/test/FakeVehicleHardwareTest.cpp
@@ -154,7 +154,7 @@
         return toInt(result.error());
     }
 
-    void onSetValues(const std::vector<SetValueResult> results) {
+    void onSetValues(std::vector<SetValueResult> results) {
         for (auto& result : results) {
             mSetValueResults.push_back(result);
         }
@@ -162,7 +162,7 @@
 
     const std::vector<SetValueResult>& getSetValueResults() { return mSetValueResults; }
 
-    void onGetValues(const std::vector<GetValueResult> results) {
+    void onGetValues(std::vector<GetValueResult> results) {
         for (auto& result : results) {
             mGetValueResults.push_back(result);
         }
@@ -170,7 +170,7 @@
 
     const std::vector<GetValueResult>& getGetValueResults() { return mGetValueResults; }
 
-    void onPropertyChangeEvent(const std::vector<VehiclePropValue>& values) {
+    void onPropertyChangeEvent(std::vector<VehiclePropValue> values) {
         for (auto& value : values) {
             mChangedProperties.push_back(value);
         }
diff --git a/automotive/vehicle/aidl/impl/vhal/Android.bp b/automotive/vehicle/aidl/impl/vhal/Android.bp
index 454fea5..a54ab4b 100644
--- a/automotive/vehicle/aidl/impl/vhal/Android.bp
+++ b/automotive/vehicle/aidl/impl/vhal/Android.bp
@@ -56,6 +56,7 @@
     srcs: [
         "src/ConnectedClient.cpp",
         "src/DefaultVehicleHal.cpp",
+        "src/PendingRequestPool.cpp",
     ],
     static_libs: [
         "VehicleHalUtils",
diff --git a/automotive/vehicle/aidl/impl/vhal/include/DefaultVehicleHal.h b/automotive/vehicle/aidl/impl/vhal/include/DefaultVehicleHal.h
index 4ee3ee9..f6f7d80 100644
--- a/automotive/vehicle/aidl/impl/vhal/include/DefaultVehicleHal.h
+++ b/automotive/vehicle/aidl/impl/vhal/include/DefaultVehicleHal.h
@@ -88,12 +88,17 @@
             GetSetValuesClient<::aidl::android::hardware::automotive::vehicle::SetValueResult,
                                ::aidl::android::hardware::automotive::vehicle::SetValueResults>;
 
+    // The default timeout of get or set value requests is 30s.
+    // TODO(b/214605968): define TIMEOUT_IN_NANO in IVehicle and allow getValues/setValues/subscribe
+    // to specify custom timeouts.
+    static constexpr int64_t TIMEOUT_IN_NANO = 30'000'000'000;
     const std::unique_ptr<IVehicleHardware> mVehicleHardware;
 
     // mConfigsByPropId and mConfigFile are only modified during initialization, so no need to
     // lock guard them.
     std::unordered_map<int32_t, ::aidl::android::hardware::automotive::vehicle::VehiclePropConfig>
             mConfigsByPropId;
+    // Only modified in constructor, so thread-safe.
     std::unique_ptr<::ndk::ScopedFileDescriptor> mConfigFile;
 
     std::mutex mLock;
diff --git a/automotive/vehicle/aidl/impl/vhal/include/PendingRequestPool.h b/automotive/vehicle/aidl/impl/vhal/include/PendingRequestPool.h
new file mode 100644
index 0000000..6dcfaff
--- /dev/null
+++ b/automotive/vehicle/aidl/impl/vhal/include/PendingRequestPool.h
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2021 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 android_hardware_automotive_vehicle_aidl_impl_vhal_include_PendingRequestPool_H_
+#define android_hardware_automotive_vehicle_aidl_impl_vhal_include_PendingRequestPool_H_
+
+#include <android-base/result.h>
+#include <android-base/thread_annotations.h>
+
+#include <atomic>
+#include <list>
+#include <mutex>
+#include <thread>
+#include <unordered_map>
+#include <unordered_set>
+
+namespace android {
+namespace hardware {
+namespace automotive {
+namespace vehicle {
+
+// A thread-safe pending request pool that tracks whether each request has timed-out.
+class PendingRequestPool final {
+  public:
+    using TimeoutCallbackFunc = std::function<void(const std::unordered_set<int64_t>&)>;
+
+    explicit PendingRequestPool(int64_t timeoutInSec);
+
+    ~PendingRequestPool();
+
+    // Adds a list of requests to the request pool.
+    // The clientId is the key for all the requests. It could be a number or an address to a data
+    // structure that represents a client. The caller must maintain this data structure.
+    // All the request IDs must be unique for one client, if any of the requestIds is duplicate with
+    // any pending request IDs for the client, this function returns error and no requests would be
+    // added. Otherwise, they would be added to the request pool.
+    // The callback would be called if requests are not finished within {@code mTimeoutInNano}
+    // seconds.
+    android::base::Result<void> addRequests(const void* clientId,
+                                            const std::unordered_set<int64_t>& requestIds,
+                                            std::shared_ptr<TimeoutCallbackFunc> callback);
+
+    // Checks whether the request is currently pending.
+    bool isRequestPending(const void* clientId, int64_t requestId) const;
+
+    // Tries to mark the requests as finished and remove them from the pool if the request is
+    // currently pending. Returns the list of request that is pending and has been finished
+    // successfully. This function would try to finish any valid requestIds even though some of the
+    // requestIds are not valid.
+    std::unordered_set<int64_t> tryFinishRequests(const void* clientId,
+                                                  const std::unordered_set<int64_t>& requestIds);
+
+    // Returns how many pending requests in the pool, for testing purpose.
+    size_t countPendingRequests(const void* clientId) const;
+
+  private:
+    // The maximum number of pending requests allowed per client. If exceeds this number, adding
+    // more requests would fail. This is to prevent spamming from client.
+    static constexpr size_t MAX_PENDING_REQUEST_PER_CLIENT = 10000;
+
+    struct PendingRequest {
+        std::unordered_set<int64_t> requestIds;
+        int64_t timeoutTimestamp;
+        std::shared_ptr<TimeoutCallbackFunc> callback;
+    };
+
+    int64_t mTimeoutInNano;
+    mutable std::mutex mLock;
+    std::unordered_map<const void*, std::list<PendingRequest>> mPendingRequestsByClient
+            GUARDED_BY(mLock);
+    std::thread mThread;
+    std::atomic<bool> mThreadStop = false;
+    std::condition_variable mCv;
+    std::mutex mCvLock;
+
+    bool isRequestPendingLocked(const void* clientId, int64_t requestId) const REQUIRES(mLock);
+
+    // Checks whether the requests in the pool has timed-out, run periodically in a separate thread.
+    void checkTimeout();
+};
+
+}  // namespace vehicle
+}  // namespace automotive
+}  // namespace hardware
+}  // namespace android
+
+#endif  // android_hardware_automotive_vehicle_aidl_impl_vhal_include_PendingRequestPool_H_
diff --git a/automotive/vehicle/aidl/impl/vhal/src/PendingRequestPool.cpp b/automotive/vehicle/aidl/impl/vhal/src/PendingRequestPool.cpp
new file mode 100644
index 0000000..c2d6f89
--- /dev/null
+++ b/automotive/vehicle/aidl/impl/vhal/src/PendingRequestPool.cpp
@@ -0,0 +1,220 @@
+/*
+ * Copyright (C) 2021 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 "PendingRequestPool.h"
+
+#include <VehicleHalTypes.h>
+#include <VehicleUtils.h>
+
+#include <utils/Log.h>
+#include <utils/SystemClock.h>
+
+#include <vector>
+
+namespace android {
+namespace hardware {
+namespace automotive {
+namespace vehicle {
+
+namespace {
+
+using ::aidl::android::hardware::automotive::vehicle::StatusCode;
+using ::android::base::Error;
+using ::android::base::Result;
+
+// At least check every 1s.
+constexpr int64_t CHECK_TIME_IN_NANO = 1000000000;
+
+}  // namespace
+
+PendingRequestPool::PendingRequestPool(int64_t timeoutInNano)
+    : mTimeoutInNano(timeoutInNano), mThread([this] {
+          // [this] must be alive within this thread because destructor would wait for this thread
+          // to exit.
+          int64_t sleepTime = std::min(mTimeoutInNano, static_cast<int64_t>(CHECK_TIME_IN_NANO));
+          std::unique_lock<std::mutex> lk(mCvLock);
+          while (!mCv.wait_for(lk, std::chrono::nanoseconds(sleepTime),
+                               [this] { return mThreadStop.load(); })) {
+              checkTimeout();
+          }
+      }) {}
+
+PendingRequestPool::~PendingRequestPool() {
+    mThreadStop = true;
+    mCv.notify_all();
+    if (mThread.joinable()) {
+        mThread.join();
+    }
+
+    // If this pool is being destructed, send out all pending requests as timeout.
+    {
+        std::scoped_lock<std::mutex> lockGuard(mLock);
+
+        for (auto& [_, pendingRequests] : mPendingRequestsByClient) {
+            for (const auto& request : pendingRequests) {
+                (*request.callback)(request.requestIds);
+            }
+        }
+        mPendingRequestsByClient.clear();
+    }
+}
+
+Result<void> PendingRequestPool::addRequests(const void* clientId,
+                                             const std::unordered_set<int64_t>& requestIds,
+                                             std::shared_ptr<TimeoutCallbackFunc> callback) {
+    std::scoped_lock<std::mutex> lockGuard(mLock);
+    std::list<PendingRequest>* pendingRequests;
+    size_t pendingRequestCount = 0;
+    if (mPendingRequestsByClient.find(clientId) != mPendingRequestsByClient.end()) {
+        pendingRequests = &mPendingRequestsByClient[clientId];
+        for (const auto& pendingRequest : *pendingRequests) {
+            const auto& pendingRequestIds = pendingRequest.requestIds;
+            for (int64_t requestId : requestIds) {
+                if (pendingRequestIds.find(requestId) != pendingRequestIds.end()) {
+                    return Error(toInt(StatusCode::INVALID_ARG))
+                           << "duplicate request ID: " << requestId;
+                }
+            }
+            pendingRequestCount += pendingRequestIds.size();
+        }
+    } else {
+        // Create a new empty list for this client.
+        pendingRequests = &mPendingRequestsByClient[clientId];
+    }
+
+    if (requestIds.size() > MAX_PENDING_REQUEST_PER_CLIENT - pendingRequestCount) {
+        return Error(toInt(StatusCode::TRY_AGAIN)) << "too many pending requests";
+    }
+
+    int64_t currentTime = elapsedRealtimeNano();
+    int64_t timeoutTimestamp = currentTime + mTimeoutInNano;
+
+    pendingRequests->push_back({
+            .requestIds = std::unordered_set<int64_t>(requestIds.begin(), requestIds.end()),
+            .timeoutTimestamp = timeoutTimestamp,
+            .callback = callback,
+    });
+
+    return {};
+}
+
+bool PendingRequestPool::isRequestPending(const void* clientId, int64_t requestId) const {
+    std::scoped_lock<std::mutex> lockGuard(mLock);
+
+    return isRequestPendingLocked(clientId, requestId);
+}
+
+size_t PendingRequestPool::countPendingRequests(const void* clientId) const {
+    std::scoped_lock<std::mutex> lockGuard(mLock);
+
+    auto it = mPendingRequestsByClient.find(clientId);
+    if (it == mPendingRequestsByClient.end()) {
+        return 0;
+    }
+
+    size_t count = 0;
+    for (const auto& pendingRequest : it->second) {
+        count += pendingRequest.requestIds.size();
+    }
+
+    return count;
+}
+
+bool PendingRequestPool::isRequestPendingLocked(const void* clientId, int64_t requestId) const {
+    auto it = mPendingRequestsByClient.find(clientId);
+    if (it == mPendingRequestsByClient.end()) {
+        return false;
+    }
+    for (const auto& pendingRequest : it->second) {
+        const auto& requestIds = pendingRequest.requestIds;
+        if (requestIds.find(requestId) != requestIds.end()) {
+            return true;
+        }
+    }
+    return false;
+}
+
+void PendingRequestPool::checkTimeout() {
+    std::vector<PendingRequest> timeoutRequests;
+    {
+        std::scoped_lock<std::mutex> lockGuard(mLock);
+
+        int64_t currentTime = elapsedRealtimeNano();
+
+        std::vector<const void*> clientsWithEmptyRequests;
+
+        for (auto& [clientId, pendingRequests] : mPendingRequestsByClient) {
+            auto it = pendingRequests.begin();
+            while (it != pendingRequests.end()) {
+                if (it->timeoutTimestamp >= currentTime) {
+                    break;
+                }
+                timeoutRequests.push_back(std::move(*it));
+                it = pendingRequests.erase(it);
+            }
+
+            if (pendingRequests.empty()) {
+                clientsWithEmptyRequests.push_back(clientId);
+            }
+        }
+
+        for (const void* clientId : clientsWithEmptyRequests) {
+            mPendingRequestsByClient.erase(clientId);
+        }
+    }
+
+    // Call the callback outside the lock.
+    for (const auto& request : timeoutRequests) {
+        (*request.callback)(request.requestIds);
+    }
+}
+
+std::unordered_set<int64_t> PendingRequestPool::tryFinishRequests(
+        const void* clientId, const std::unordered_set<int64_t>& requestIds) {
+    std::scoped_lock<std::mutex> lockGuard(mLock);
+
+    std::unordered_set<int64_t> foundIds;
+
+    if (mPendingRequestsByClient.find(clientId) == mPendingRequestsByClient.end()) {
+        return foundIds;
+    }
+
+    auto& pendingRequests = mPendingRequestsByClient[clientId];
+    auto it = pendingRequests.begin();
+    while (it != pendingRequests.end()) {
+        auto& pendingRequestIds = it->requestIds;
+        for (int64_t requestId : requestIds) {
+            auto idIt = pendingRequestIds.find(requestId);
+            if (idIt == pendingRequestIds.end()) {
+                continue;
+            }
+            pendingRequestIds.erase(idIt);
+            foundIds.insert(requestId);
+        }
+        if (pendingRequestIds.empty()) {
+            it = pendingRequests.erase(it);
+            continue;
+        }
+        it++;
+    }
+
+    return foundIds;
+}
+
+}  // namespace vehicle
+}  // namespace automotive
+}  // namespace hardware
+}  // namespace android
diff --git a/automotive/vehicle/aidl/impl/vhal/test/PendingRequestPoolTest.cpp b/automotive/vehicle/aidl/impl/vhal/test/PendingRequestPoolTest.cpp
new file mode 100644
index 0000000..03d795b
--- /dev/null
+++ b/automotive/vehicle/aidl/impl/vhal/test/PendingRequestPoolTest.cpp
@@ -0,0 +1,274 @@
+/*
+ * Copyright (C) 2021 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 "PendingRequestPool.h"
+
+#include <VehicleHalTypes.h>
+#include <VehicleUtils.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <unordered_set>
+#include <vector>
+
+namespace android {
+namespace hardware {
+namespace automotive {
+namespace vehicle {
+
+using ::aidl::android::hardware::automotive::vehicle::StatusCode;
+
+using ::testing::ElementsAre;
+using ::testing::UnorderedElementsAre;
+using ::testing::WhenSorted;
+
+class PendingRequestPoolTest : public ::testing::Test {
+  public:
+    void SetUp() override { mPool = std::make_unique<PendingRequestPool>(TEST_TIMEOUT); }
+
+    void TearDown() override {
+        if (mPool != nullptr) {
+            ASSERT_EQ(mPool->countPendingRequests(getTestClientId()), static_cast<size_t>(0))
+                    << "at least one pending request still exists in the pool when finish";
+        }
+    }
+
+    PendingRequestPool* getPool() { return mPool.get(); }
+
+    void destroyPool() { mPool.reset(); }
+
+    int64_t getTimeout() { return TEST_TIMEOUT; }
+
+    void* getTestClientId() { return reinterpret_cast<void*>(0); }
+
+  private:
+    // Test timeout is 0.1s.
+    static const int64_t TEST_TIMEOUT = 100000000;
+
+    std::unique_ptr<PendingRequestPool> mPool;
+};
+
+TEST_F(PendingRequestPoolTest, testFinishAllRequests) {
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    std::unordered_set<int64_t> requestIds;
+    for (int64_t i = 0; i < 10; i++) {
+        requestIds.insert(i);
+    }
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), requestIds, callback));
+
+    for (int64_t i = 0; i < 10; i++) {
+        ASSERT_TRUE(getPool()->isRequestPending(getTestClientId(), i));
+    }
+
+    for (int64_t i = 0; i < 10; i++) {
+        ASSERT_THAT(getPool()->tryFinishRequests(getTestClientId(), {i}), UnorderedElementsAre(i));
+    }
+
+    for (int64_t i = 0; i < 10; i++) {
+        ASSERT_FALSE(getPool()->isRequestPending(getTestClientId(), i));
+    }
+}
+
+TEST_F(PendingRequestPoolTest, testFinishHalfOfRequest) {
+    int64_t timeout = getTimeout();
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    std::unordered_set<int64_t> requestIds;
+    for (int64_t i = 0; i < 10; i++) {
+        requestIds.insert(i);
+    }
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), requestIds, callback));
+
+    for (int64_t i = 0; i < 10; i++) {
+        ASSERT_TRUE(getPool()->isRequestPending(getTestClientId(), i));
+    }
+
+    // Finish half of the requests.
+    requestIds.clear();
+    for (int64_t i = 0; i < 5; i++) {
+        requestIds.insert(i);
+    }
+
+    ASSERT_EQ(getPool()->tryFinishRequests(getTestClientId(), requestIds), requestIds);
+
+    for (int64_t i = 0; i < 5; i++) {
+        ASSERT_FALSE(getPool()->isRequestPending(getTestClientId(), i));
+    }
+    for (int64_t i = 5; i < 10; i++) {
+        ASSERT_TRUE(getPool()->isRequestPending(getTestClientId(), i));
+    }
+
+    // Wait until the unfinished requests timeout. The check interval is timeout, so at max we
+    // would wait an additional interval, which is 2 * timeout until the callback is called.
+    std::this_thread::sleep_for(2 * std::chrono::nanoseconds(timeout));
+
+    ASSERT_THAT(timeoutRequestIds, WhenSorted(ElementsAre(5, 6, 7, 8, 9)));
+}
+
+TEST_F(PendingRequestPoolTest, testFinishRequestTwice) {
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), {0}, callback));
+
+    ASSERT_THAT(getPool()->tryFinishRequests(getTestClientId(), {0}), UnorderedElementsAre(0))
+            << "failed to finish an added request";
+    ASSERT_TRUE(getPool()->tryFinishRequests(getTestClientId(), {0}).empty())
+            << "finish a request second time must return empty result";
+}
+
+TEST_F(PendingRequestPoolTest, testFinishRequestNonExistingId) {
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), {0, 1, 2}, callback));
+
+    ASSERT_THAT(getPool()->tryFinishRequests(getTestClientId(), {0, 1, 2, 3}),
+                UnorderedElementsAre(0, 1, 2))
+            << "finished request IDs must not contain non-existing request ID";
+    // Even though one of the request to finish does not exist, the rest of the requests should be
+    // finished.
+    ASSERT_EQ(getPool()->countPendingRequests(getTestClientId()), static_cast<size_t>(0))
+            << "requests not being finished correctly";
+}
+
+TEST_F(PendingRequestPoolTest, testFinishAfterTimeout) {
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), {0}, callback));
+
+    std::this_thread::sleep_for(2 * std::chrono::nanoseconds(getTimeout()));
+
+    ASSERT_TRUE(getPool()->tryFinishRequests(getTestClientId(), {0}).empty())
+            << "finish a request after timeout must do nothing";
+}
+
+TEST_F(PendingRequestPoolTest, testDestroyWithPendingRequests) {
+    std::mutex lock;
+    std::vector<int64_t> timeoutRequestIds;
+
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [&lock, &timeoutRequestIds](const std::unordered_set<int64_t>& requests) {
+                std::scoped_lock<std::mutex> lockGuard(lock);
+                for (int64_t request : requests) {
+                    timeoutRequestIds.push_back(request);
+                }
+            });
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), {0}, callback));
+
+    destroyPool();
+
+    // Before the pool is destroyed, the pending requests should be notified as timeout.
+    ASSERT_THAT(timeoutRequestIds, UnorderedElementsAre(0))
+            << "timeout not triggered when the pool is destroyed";
+}
+
+TEST_F(PendingRequestPoolTest, testDuplicateRequestId) {
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [](std::unordered_set<int64_t>) {});
+
+    ASSERT_RESULT_OK(getPool()->addRequests(getTestClientId(), {0}, callback));
+    ASSERT_FALSE(getPool()->addRequests(getTestClientId(), {1, 2, 0}, callback).ok())
+            << "adding duplicate request IDs must fail";
+
+    ASSERT_THAT(getPool()->tryFinishRequests(getTestClientId(), {0}), UnorderedElementsAre(0));
+}
+
+TEST_F(PendingRequestPoolTest, testSameRequestIdForDifferentClient) {
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [](std::unordered_set<int64_t>) {});
+
+    ASSERT_RESULT_OK(getPool()->addRequests(reinterpret_cast<void*>(0), {0}, callback));
+    ASSERT_RESULT_OK(getPool()->addRequests(reinterpret_cast<void*>(1), {1, 2, 0}, callback));
+
+    ASSERT_THAT(getPool()->tryFinishRequests(reinterpret_cast<void*>(0), {0}),
+                UnorderedElementsAre(0));
+    ASSERT_THAT(getPool()->tryFinishRequests(reinterpret_cast<void*>(1), {1, 2, 0}),
+                UnorderedElementsAre(0, 1, 2));
+}
+
+TEST_F(PendingRequestPoolTest, testPendingRequestCountLimit) {
+    auto callback = std::make_shared<PendingRequestPool::TimeoutCallbackFunc>(
+            [](std::unordered_set<int64_t>) {});
+
+    std::unordered_set<int64_t> requests;
+
+    // MAX_PENDING_REQUEST_PER_CLIENT = 10000
+    for (size_t i = 0; i < 10000; i++) {
+        requests.insert(static_cast<int64_t>(i));
+    }
+    ASSERT_RESULT_OK(getPool()->addRequests(reinterpret_cast<void*>(0), requests, callback));
+
+    auto result = getPool()->addRequests(reinterpret_cast<void*>(0), {static_cast<int64_t>(10000)},
+                                         callback);
+    ASSERT_FALSE(result.ok()) << "adding more pending requests than limit must fail";
+    ASSERT_EQ(result.error().code(), toInt(StatusCode::TRY_AGAIN));
+
+    getPool()->tryFinishRequests(reinterpret_cast<void*>(0), requests);
+}
+
+}  // namespace vehicle
+}  // namespace automotive
+}  // namespace hardware
+}  // namespace android