use an intrusive linked list for peer_cache_entry instead an unordered set, to avoid heap allocations and make cache operations not able to fail. This simplifies error handling

include/libtorrent/aux_/storage_piece_set.hpp

@@ -33,9 +33,12 @@ POSSIBILITY OF SUCH DAMAGE.
 #ifndef TORRENT_STORAGE_PIECE_SET_HPP_INCLUDE
 #define TORRENT_STORAGE_PIECE_SET_HPP_INCLUDE
 
-#include <unordered_set>
+#include "libtorrent/aux_/disable_warnings_push.hpp"
+#include <boost/intrusive/list.hpp>
+#include "libtorrent/aux_/disable_warnings_pop.hpp"
 
 #include "libtorrent/export.hpp"
+#include "libtorrent/block_cache.hpp" // for cached_piece_entry
 
 namespace libtorrent {
 
@@ -49,15 +52,16 @@ namespace aux {
 	// specific torrent
 	struct TORRENT_EXPORT storage_piece_set
 	{
+		using list_t = boost::intrusive::list<cached_piece_entry, boost::intrusive::constant_time_size<false>>;
 		void add_piece(cached_piece_entry* p);
 		void remove_piece(cached_piece_entry* p);
-		bool has_piece(cached_piece_entry const* p) const;
-		int num_pieces() const { return int(m_cached_pieces.size()); }
-		std::unordered_set<cached_piece_entry*> const& cached_pieces() const
+		int num_pieces() const { return m_num_pieces; }
+		list_t const& cached_pieces() const
 		{ return m_cached_pieces; }
 	private:
 		// these are cached pieces belonging to this storage
-		std::unordered_set<cached_piece_entry*> m_cached_pieces;
+		list_t m_cached_pieces;
+		int m_num_pieces = 0;
 	};
 }}
 

include/libtorrent/block_cache.hpp

@@ -39,6 +39,10 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <unordered_set>
 #include <array>
 
+#include "libtorrent/aux_/disable_warnings_push.hpp"
+#include <boost/intrusive/list.hpp>
+#include "libtorrent/aux_/disable_warnings_pop.hpp"
+
 #include "libtorrent/time.hpp"
 #include "libtorrent/error_code.hpp"
 #include "libtorrent/io_service_fwd.hpp"
@@ -169,12 +173,15 @@ namespace aux {
 
 	// list_node is here to be able to link this cache entry
 	// into one of the LRU lists
-	struct TORRENT_EXTRA_EXPORT cached_piece_entry : list_node<cached_piece_entry>
+	struct TORRENT_EXTRA_EXPORT cached_piece_entry
+		: list_node<cached_piece_entry>
+		, boost::intrusive::list_base_hook<boost::intrusive::link_mode<
+			boost::intrusive::auto_unlink>>
 	{
 		cached_piece_entry();
 		~cached_piece_entry();
-		cached_piece_entry(cached_piece_entry&&) noexcept = default;
-		cached_piece_entry& operator=(cached_piece_entry&&) noexcept = default;
+		cached_piece_entry(cached_piece_entry&&) = default;
+		cached_piece_entry& operator=(cached_piece_entry&&) = default;
 
 		bool ok_to_evict(bool ignore_hash = false) const
 		{
@@ -217,7 +224,7 @@ namespace aux {
 		//TODO: make this 32 bits and to count seconds since the block cache was created
 		time_point expire = min_time();
 
-		piece_index_t piece;
+		piece_index_t piece{0};
 
 		// the number of dirty blocks in this piece
 		std::uint64_t num_dirty:14;

src/block_cache.cpp

@@ -304,8 +304,7 @@ static_assert(int(job_action_name.size()) == static_cast<int>(job_action_t::num_
 #endif
 
 cached_piece_entry::cached_piece_entry()
-	: piece(0)
-	, num_dirty(0)
+	: num_dirty(0)
 	, num_blocks(0)
 	, blocks_in_piece(0)
 	, hashing(0)
@@ -1547,7 +1546,6 @@ void block_cache::check_invariant() const
 			}
 			// pieces in the ghost list are still in the storage's list of pieces,
 			// because we need to be able to evict them when stopping a torrent
-			TORRENT_PIECE_ASSERT(pe->storage->has_piece(pe), pe);
 
 			storages.insert(pe->storage.get());
 		}
@@ -1555,9 +1553,9 @@ void block_cache::check_invariant() const
 
 	for (auto s : storages)
 	{
-		for (auto pe : s->cached_pieces())
+		for (auto const& pe : s->cached_pieces())
 		{
-			TORRENT_PIECE_ASSERT(pe->storage.get() == s, pe);
+			TORRENT_PIECE_ASSERT(pe.storage.get() == s, &pe);
 		}
 	}
 
@@ -1572,8 +1570,6 @@ void block_cache::check_invariant() const
 		int num_pending = 0;
 		int num_refcount = 0;
 
-		TORRENT_ASSERT(p.storage->has_piece(&p));
-
 		for (int k = 0; k < p.blocks_in_piece; ++k)
 		{
 			if (p.blocks[k].buf)

src/disk_io_thread.cpp

@@ -888,9 +888,9 @@ constexpr disk_job_flags_t disk_interface::cache_hit;
 			piece_index.reserve(pieces.size());
 			for (auto const& p : pieces)
 			{
-				TORRENT_ASSERT(p->get_storage() == storage);
-				if (p->get_storage() != storage) continue;
-				piece_index.push_back(p->piece);
+				TORRENT_ASSERT(p.get_storage() == storage);
+				if (p.get_storage() != storage) continue;
+				piece_index.push_back(p.piece);
 			}
 
 			for (auto idx : piece_index)
@@ -910,9 +910,9 @@ constexpr disk_job_flags_t disk_interface::cache_hit;
 			if ((flags & flush_delete_cache) && (flags & flush_expect_clear))
 			{
 				auto const& storage_pieces = storage->cached_pieces();
-				for (auto p : storage_pieces)
+				for (auto const& p : storage_pieces)
 				{
-					cached_piece_entry* pe = m_disk_cache.find_piece(storage, p->piece);
+					cached_piece_entry* pe = m_disk_cache.find_piece(storage, p.piece);
 					TORRENT_PIECE_ASSERT(pe->num_dirty == 0, pe);
 				}
 			}
@@ -2639,15 +2639,15 @@ constexpr disk_job_flags_t disk_interface::cache_hit;
 				TORRENT_ASSERT(storage);
 				ret->pieces.reserve(aux::numeric_cast<std::size_t>(storage->num_pieces()));
 
-				for (auto pe : storage->cached_pieces())
+				for (auto const& pe : storage->cached_pieces())
 				{
-					TORRENT_ASSERT(pe->storage.get() == storage.get());
+					TORRENT_ASSERT(pe.storage.get() == storage.get());
 
-					if (pe->cache_state == cached_piece_entry::read_lru2_ghost
-						|| pe->cache_state == cached_piece_entry::read_lru1_ghost)
+					if (pe.cache_state == cached_piece_entry::read_lru2_ghost
+						|| pe.cache_state == cached_piece_entry::read_lru1_ghost)
 						continue;
 					ret->pieces.emplace_back();
-					get_cache_info_impl(ret->pieces.back(), pe, block_size);
+					get_cache_info_impl(ret->pieces.back(), &pe, block_size);
 				}
 			}
 			else

src/storage_piece_set.cpp

@@ -41,23 +41,18 @@ namespace libtorrent { namespace aux {
 	{
 		TORRENT_ASSERT(p->in_storage == false);
 		TORRENT_ASSERT(p->storage.get() == this);
-		TORRENT_ASSERT(m_cached_pieces.count(p) == 0);
-		m_cached_pieces.insert(p);
+		m_cached_pieces.push_back(*p);
+		++m_num_pieces;
 #if TORRENT_USE_ASSERTS
 		p->in_storage = true;
 #endif
 	}
 
-	bool storage_piece_set::has_piece(cached_piece_entry const* p) const
-	{
-		return m_cached_pieces.count(const_cast<cached_piece_entry*>(p)) > 0;
-	}
-
 	void storage_piece_set::remove_piece(cached_piece_entry* p)
 	{
 		TORRENT_ASSERT(p->in_storage == true);
-		TORRENT_ASSERT(m_cached_pieces.count(p) == 1);
-		m_cached_pieces.erase(p);
+		p->unlink();
+		--m_num_pieces;
 #if TORRENT_USE_ASSERTS
 		p->in_storage = false;
 #endif