ISubsystem

ISubsystem defines a lifecycle interface for engine components that require explicit startup and shutdown phases.

class ISubsystem
{
public:
  virtual ~ISubsystem() = default;

  virtual void start() {}
  virtual void stop() {}
};

Purpose

• Provide deterministic initialization and teardown hooks for stateful modules in the system.

Responsibilities

Method	Description
start	Called during engine bootstrapping.
stop	Called during shutdown or reset.

Notes

• Methods have default empty implementations, allowing derived classes to override only what they need.
• Used by core modules like BarAggregator, Strategy, ExecutionTracker, SymbolRegistry, etc.
• Lifecycle is typically orchestrated by the engine or test harness.
• No assumptions about threading — start/stop are always externally coordinated.

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IDrainable

IDrainable is a separate interface for components with pending async work that must complete before shutdown.

class IDrainable
{
public:
  virtual ~IDrainable() = default;
  virtual bool drain(uint32_t timeoutMs) = 0;
};

Purpose

• Wait for in-flight operations (e.g., pending orders, network requests) to complete.

When to Implement

Only implement IDrainable for components with actual async work: * Exchange connectors (in-flight order confirmations) * Order executors (pending order submissions) * Network transports (pending requests)

Do NOT implement for stateless or synchronous components like strategies, aggregators, or registries.