Refactor scheduler and base queue to use Abseil primitives

[Copilot]

Replaces STL synchronization and container primitives in the cyber scheduler and base queue with Abseil equivalents for improved cache efficiency, richer thread-safety annotations, and cleaner async patterns.

Changes

cyber/base/thread_safe_queue.h

• std::mutex + std::condition_variable → absl::Mutex + absl::MutexLock + Await()
• volatile bool break_all_wait_ → bool with ABSL_GUARDED_BY(mutex_) annotation
• Private IsReadyForDequeue() condition predicate for Await()

cyber/scheduler/scheduler.h + policy headers

• std::unordered_map → absl::flat_hash_map (Swiss table; better cache locality)
• std::mutex cr_wl_mtx_ → absl::Mutex

cyber/scheduler/scheduler*.cc

• std::lock_guard<std::mutex> on cr_wl_mtx_ → absl::WriterMutexLock
• String .append() chains → absl::StrAppend() / absl::StrCat()
• Singleton guard in scheduler_factory.cc: std::mutex → absl::Mutex

Build

• Added @com_google_absl//absl/container:flat_hash_map, absl/synchronization, and absl/strings deps to affected targets.

Example: WaitDequeue before/after

// Before
bool WaitDequeue(T* element) {
  std::unique_lock<std::mutex> lock(mutex_);
  cv_.wait(lock, [this]() { return break_all_wait_ || !queue_.empty(); });
  ...
}

// After
bool WaitDequeue(T* element) {
  absl::MutexLock lock(&mutex_);
  mutex_.Await(absl::Condition(this, &ThreadSafeQueue::IsReadyForDequeue));
  ...
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature]: Refactor the following Apollo C++ code to use Abseil and Folly for better performance.</issue_title>
<issue_description>### Use Case / Motivation

Improve the performance of the base library and ensure consistency in coding style.

Proposed Implementation

Category	Legacy / STL	Recommended Alternative	Benefits / Optimization Points
Containers	std::unordered_map	absl::flat_hash_map	Better memory usage and throughput; Abseil’s Swiss table is cache-friendly and often significantly faster than std::unordered_map.(Abseil)
Strings	std::stringstream / +	absl::StrCat / absl::StrJoin	Reduces allocations by pre-computing lengths and avoids temporary string creation, leading to faster concatenation.(php.cn)
Synchronization Primitives	std::mutex	absl::Mutex	Abseil’s Mutex can have better uncontended performance and richer features (e.g., deadlock detection and advanced waiting conditions).(AI Coding Community)
Async / Future	std::future	folly::Future / folly::SemiFuture	Supports continuation chaining (.then()), executors, and more expressive async composition than the basic C++ std::future.(DeepWiki)
Memory / Large Strings	std::vector (or naive buffers)	absl::Cord	Efficient handling of large/fragmented strings or data streams, minimizes copying, and can chain data segments.(AI Coding Community)
Error Handling	bool / int status codes	absl::StatusOr	Strongly typed status with return value; forces error checking and makes failure handling safer.(AI Coding Community)
Concurrent Queue	std::queue + std::mutex	folly::MPMCQueue	Lock-free or low-overhead multi-producer, multi-consumer queue; better throughput under high concurrency.(php.cn)

Alternatives Considered

No response</issue_description>

<agent_instructions>Task: Refactor the following Apollo C++ code to use Abseil and Folly for better performance.
Rules:

Replace std::unordered_map with absl::flat_hash_map.

Replace string concatenations with absl::StrCat.

Replace std::mutex with absl::Mutex and use absl::WriterMutexLock.

Ensure C++17 compatibility (e.g., use std::string_view where appropriate).

Avoid manual memory management; use absl::StatusOr for function returns that might fail.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature]: Refactor the following Apollo C++ code to use Abseil and Folly for better performance. #182

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