Add comments to class nano::prioritization (#3742)

* Remove drop function which is unused, even if passed in the constructor

* Mark function nano::prioritization::dump as const

* Make nano::prioritization::maximum a private member

* Add comments to class nano::prioritization

nano/node/prioritization.cpp

@@ -14,6 +14,7 @@ bool nano::prioritization::value_type::operator== (value_type const & other_a) c
 	return time == other_a.time && block->hash () == other_a.block->hash ();
 }
 
+/** Moves the bucket pointer to the next bucket */
 void nano::prioritization::next ()
 {
 	++current;
@@ -23,6 +24,7 @@ void nano::prioritization::next ()
 	}
 }
 
+/** Seek to the next non-empty bucket, if one exists */
 void nano::prioritization::seek ()
 {
 	next ();
@@ -32,6 +34,7 @@ void nano::prioritization::seek ()
 	}
 }
 
+/** Initialise the schedule vector */
 void nano::prioritization::populate_schedule ()
 {
 	for (auto i = 0; i < buckets.size (); ++i)
@@ -40,8 +43,11 @@ void nano::prioritization::populate_schedule ()
 	}
 }
 
-nano::prioritization::prioritization (uint64_t maximum, std::function<void (std::shared_ptr<nano::block>)> const & drop_a) :
-	drop{ drop_a },
+/**
+ * Prioritization constructor, construct a container containing approximately 'maximum' number of blocks.
+ * @param maximum number of blocks that this container can hold, this is a soft and approximate limit.
+ */
+nano::prioritization::prioritization (uint64_t maximum) :
 	maximum{ maximum }
 {
 	static std::size_t constexpr bucket_count = 129;
@@ -57,6 +63,10 @@ nano::prioritization::prioritization (uint64_t maximum, std::function<void (std:
 	current = schedule.begin ();
 }
 
+/**
+ * Push a block and its associated time into the prioritization container.
+ * The time is given here because sideband might not exist in the case of state blocks.
+ */
 void nano::prioritization::push (uint64_t time, std::shared_ptr<nano::block> block)
 {
 	auto was_empty = empty ();
@@ -76,6 +86,7 @@ void nano::prioritization::push (uint64_t time, std::shared_ptr<nano::block> blo
 	}
 }
 
+/** Return the highest priority block of the current bucket */
 std::shared_ptr<nano::block> nano::prioritization::top () const
 {
 	debug_assert (!empty ());
@@ -84,6 +95,7 @@ std::shared_ptr<nano::block> nano::prioritization::top () const
 	return result;
 }
 
+/** Pop the current block from the container and seek to the next block, if it exists */
 void nano::prioritization::pop ()
 {
 	debug_assert (!empty ());
@@ -93,6 +105,7 @@ void nano::prioritization::pop ()
 	seek ();
 }
 
+/** Returns the total number of blocks in buckets */
 std::size_t nano::prioritization::size () const
 {
 	std::size_t result{ 0 };
@@ -103,22 +116,26 @@ std::size_t nano::prioritization::size () const
 	return result;
 }
 
+/** Returns number of buckets, 129 by default */
 std::size_t nano::prioritization::bucket_count () const
 {
 	return buckets.size ();
 }
 
+/** Returns number of items in bucket with index 'index' */
 std::size_t nano::prioritization::bucket_size (std::size_t index) const
 {
 	return buckets[index].size ();
 }
 
+/** Returns true if all buckets are empty */
 bool nano::prioritization::empty () const
 {
 	return std::all_of (buckets.begin (), buckets.end (), [] (priority const & bucket_a) { return bucket_a.empty (); });
 }
 
-void nano::prioritization::dump ()
+/** Print the state of the class in stderr */
+void nano::prioritization::dump () const
 {
 	for (auto const & i : buckets)
 	{

nano/node/prioritization.hpp

@@ -9,6 +9,17 @@
 namespace nano
 {
 class block;
+
+/** A container for holding blocks and their arrival/creation time.
+ *
+ *  The container consists of a number of buckets. Each bucket holds an ordered set of 'value_type' items.
+ *  The buckets are accessed in a round robin fashion. The index 'current' holds the index of the bucket to access next.
+ *  When a block is inserted, the bucket to go into is determined by the account balance and the priority inside that
+ *  bucket is determined by its creation/arrival time.
+ *
+ *  The arrival/creation time is only an approximation and it could even be wildly wrong,
+ *  for example, in the event of bootstrapped blocks.
+ */
 class prioritization final
 {
 	class value_type
@@ -19,19 +30,31 @@ class prioritization final
 		bool operator< (value_type const & other_a) const;
 		bool operator== (value_type const & other_a) const;
 	};
+
 	using priority = std::set<value_type>;
+
+	/** container for the buckets to be read in round robin fashion */
 	std::vector<priority> buckets;
+
+	/** thresholds that define the bands for each bucket, the minimum balance an account must have to enter a bucket,
+	 *  the container writes a block to the lowest indexed bucket that has balance larger than the bucket's minimum value */
 	std::vector<nano::uint128_t> minimums;
+
+	/** Contains bucket indicies to iterate over when making the next scheduling decision */
+	std::vector<uint8_t> schedule;
+
+	/** index of bucket to read next */
+	decltype (schedule)::const_iterator current;
+
+	/** maximum number of blocks in whole container, each bucket's maximum is maximum / bucket_number */
+	uint64_t const maximum;
+
 	void next ();
 	void seek ();
 	void populate_schedule ();
-	std::function<void (std::shared_ptr<nano::block>)> drop;
-	// Contains bucket indicies to iterate over when making the next scheduling decision
-	std::vector<uint8_t> schedule;
-	decltype (schedule)::const_iterator current;
 
 public:
-	prioritization (uint64_t maximum = 250000u, std::function<void (std::shared_ptr<nano::block>)> const & drop_a = nullptr);
+	prioritization (uint64_t maximum = 250000u);
 	void push (uint64_t time, std::shared_ptr<nano::block> block);
 	std::shared_ptr<nano::block> top () const;
 	void pop ();
@@ -39,8 +62,7 @@ public:
 	std::size_t bucket_count () const;
 	std::size_t bucket_size (std::size_t index) const;
 	bool empty () const;
-	void dump ();
-	uint64_t const maximum;
+	void dump () const;
 
 	std::unique_ptr<nano::container_info_component> collect_container_info (std::string const &);
 };