Document Timeout

lib/base/io-engine.cpp

@@ -146,6 +146,11 @@ void AsioConditionVariable::Wait(boost::asio::yield_context yc)
 	m_Timer.async_wait(yc[ec]);
 }
 
+/**
+ * Cancels any pending timeout callback.
+ *
+ * Must be called in the strand in which the callback was scheduled!
+ */
 void Timeout::Cancel()
 {
 	m_Cancelled->store(true);

lib/base/io-engine.hpp

@@ -165,6 +165,22 @@ private:
 /**
  * I/O timeout emulator
  *
+ * This class provides a workaround for Boost.ASIO's lack of built-in timeout support.
+ * While Boost.ASIO handles asynchronous operations, it does not natively support timeouts for these operations.
+ * This class uses a boost::asio::deadline_timer to emulate a timeout by scheduling a callback to be triggered
+ * after a specified duration, effectively adding timeout behavior where none exists.
+ * The callback is executed within the provided strand, ensuring thread-safety.
+ *
+ * The constructor returns immediately after scheduling the timeout callback.
+ * The callback itself is invoked asynchronously when the timeout occurs.
+ * This allows the caller to continue execution while the timeout is running in the background.
+ *
+ * The class provides a Cancel() method to unschedule any pending callback. If the callback has already been run,
+ * calling Cancel() has no effect. This method can be used to abort the timeout early if the monitored operation
+ * completes before the callback has been run. The Timeout destructor also automatically cancels any pending callback.
+ * A callback is considered pending even if the timeout has already expired,
+ * but the callback has not been executed yet due to a busy strand.
+ *
  * @ingroup base
  */
 class Timeout
@@ -172,6 +188,14 @@ class Timeout
 public:
 	using Timer = boost::asio::deadline_timer;
 
+	/**
+	 * Schedules onTimeout to be triggered after timeoutFromNow on strand.
+	 *
+	 * @param strand The strand in which the callback will be executed.
+	 *				 The caller must also run in this strand, as well as Cancel() and the destructor!
+	 * @param timeoutFromNow The duration after which the timeout callback will be triggered.
+	 * @param onTimeout The callback to invoke when the timeout occurs.
+	 */
 	template<class OnTimeout>
 	Timeout(boost::asio::io_context::strand& strand, const Timer::duration_type& timeoutFromNow, OnTimeout onTimeout)
 		: m_Timer(strand.context(), timeoutFromNow), m_Cancelled(Shared<Atomic<bool>>::Make(false))
@@ -192,6 +216,11 @@ public:
 	Timeout& operator=(const Timeout&) = delete;
 	Timeout& operator=(Timeout&&) = delete;
 
+	/**
+	 * Cancels any pending timeout callback.
+	 *
+	 * Must be called in the strand in which the callback was scheduled!
+	 */
 	~Timeout()
 	{
 		Cancel();
@@ -201,6 +230,14 @@ public:
 
 private:
 	Timer m_Timer;
+
+	/**
+	 * Indicates whether the Timeout has been cancelled.
+	 *
+	 * This must be Shared<> between the lambda in the constructor and Cancel() for the case
+	 * the destructor calls Cancel() while the lambda is already queued in the strand.
+	 * The whole Timeout instance can't be kept alive by the lambda because this would delay the destructor.
+	 */
 	Shared<Atomic<bool>>::Ptr m_Cancelled;
 };