refactor: Migrate to folly::available_concurrency

[yfeldblum]

The name hardware_concurrency, while parallel to std::thread::hardware_concurrency, may be misleading. Migrate to the name available_concurrency.

== NO RELEASE NOTE ==

Summary by Sourcery

Standardize concurrency detection on folly::available_concurrency across the Presto C++ server, configuration utilities, and related tests.

Enhancements:

• Replace uses of folly::hardware_concurrency with folly::available_concurrency in server initialization, overload checks, and connector thread pool sizing.
• Update the hardwareConcurrency helper to wrap folly::available_concurrency with validation to ensure a non-zero result.

Tests:

• Adjust existing configuration and server operation tests to assert against folly::available_concurrency-based values.
• Update trace tool replayer tests to construct thread pool executors using folly::available_concurrency.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Refactors the server and tests to use folly::available_concurrency() instead of folly::hardware_concurrency() everywhere, keeping configuration and thread-pool sizing logic otherwise identical.

Class diagram for usage of folly_available_concurrency in PrestoServer and Configs

classDiagram
  class PrestoServer {
    +void initializeThreadPools()
    +void checkOverload()
    +protocol_NodeStatus fetchNodeStatus()
  }

  class Configs {
    +static uint32_t hardwareConcurrency()
  }

  class FollyRuntime {
    +static size_t available_concurrency()
  }

  PrestoServer ..> FollyRuntime : uses_available_concurrency
  Configs ..> FollyRuntime : uses_available_concurrency
  PrestoServer ..> Configs : may_call_hardwareConcurrency

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Flow diagram for thread pool sizing using folly_available_concurrency

flowchart TD
  Start([Start initializeThreadPools]) --> GetConfig[Get SystemConfig_instance]
  GetConfig --> GetHw[hwConcurrency = folly_available_concurrency]
  GetHw --> DriverCpu["Compute numDriverCpuThreads = max(driverMultiplier * hwConcurrency, 1)"]
  DriverCpu --> ExchangeIo["Compute numExchangeHttpClientIoThreads = max(exchangeIoMultiplier * folly_available_concurrency, 1)"]
  ExchangeIo --> ExchangeCpu["Compute numExchangeHttpClientCpuThreads = max(exchangeCpuMultiplier * folly_available_concurrency, 1)"]
  ExchangeCpu --> ConnectorCpu["Compute numConnectorCpuThreads = max(connectorCpuMultiplier * folly_available_concurrency, 0)"]
  ConnectorCpu --> ConnectorIo["Compute numConnectorIoThreads = max(connectorIoMultiplier * folly_available_concurrency, 0)"]
  ConnectorIo --> End([Create thread pool executors with computed sizes])

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File-Level Changes

Change	Details	Files
Use folly::available_concurrency() instead of folly::hardware_concurrency() for thread-pool sizing, overload checks, configuration defaults, and tests.	Update PrestoServer thread-pool and overload-threshold calculations to call folly::available_concurrency() while preserving existing multipliers and bounds. Adjust hardwareConcurrency() helper to delegate to folly::available_concurrency() and update its documentation comment accordingly. Update tests that assert on concurrency-derived values to expect folly::available_concurrency() results instead of folly::hardware_concurrency(). Change CPU thread pool executors in trace-related tests to be constructed with folly::available_concurrency().	presto-native-execution/presto_cpp/main/PrestoServer.cpp presto-native-execution/presto_cpp/main/common/Configs.cpp presto-native-execution/presto_cpp/main/tests/ServerOperationTest.cpp presto-native-execution/presto_cpp/main/common/tests/ConfigTest.cpp presto-native-execution/presto_cpp/main/tool/trace/tests/BroadcastWriteReplayerTest.cpp presto-native-execution/presto_cpp/main/tool/trace/tests/PartitionAndSerializeReplayerTest.cpp

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[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• In PrestoServer::checkOverload, hwConcurrency is now derived from folly::available_concurrency() but still cached in a static const—if available_concurrency is meant to reflect dynamic limits (e.g., cgroup/numa changes), consider recomputing it each time instead of storing it statically so overload thresholds stay aligned with the current environment.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `PrestoServer::checkOverload`, `hwConcurrency` is now derived from `folly::available_concurrency()` but still cached in a `static const`—if `available_concurrency` is meant to reflect dynamic limits (e.g., cgroup/numa changes), consider recomputing it each time instead of storing it statically so overload thresholds stay aligned with the current environment.

## Individual Comments

### Comment 1
<location path="presto-native-execution/presto_cpp/main/PrestoServer.cpp" line_range="1710" />
<code_context>
   }

-  static const auto hwConcurrency = folly::hardware_concurrency();
+  static const auto hwConcurrency = folly::available_concurrency();
   const auto overloadedThresholdCpuPct =
       systemConfig->workerOverloadedThresholdCpuPct();
</code_context>
<issue_to_address>
**issue:** Guard against available_concurrency() returning 0 when computing overload thresholds.

At other call sites you wrap `folly::available_concurrency()` in `std::max(..., 1)`, but here the static `hwConcurrency` feeds directly into the overload logic. If `available_concurrency()` returns 0 (as noted in `hardwareConcurrency()`), `overloadedThresholdQueuedDrivers` becomes 0 and overload detection effectively stops working. Please normalize this value here (e.g., `std::max<size_t>(folly::available_concurrency(), 1)` or by using `hardwareConcurrency()`).
</issue_to_address>

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