add new multi-threaded disk I/O subsystem using preadv and pwritev

CMakeLists.txt

@@ -165,6 +165,8 @@ set(libtorrent_aux_include_files
 	disable_warnings_pop.hpp
 	disable_warnings_push.hpp
 	disk_buffer_pool.hpp
+	disk_cache.hpp
+	visit_block_iovecs.hpp
 	disk_completed_queue.hpp
 	mmap_disk_job.hpp
 	disk_job.hpp
@@ -225,6 +227,7 @@ set(libtorrent_aux_include_files
 	portmap.hpp
 	posix_part_file.hpp
 	posix_storage.hpp
+	pread_disk_job.hpp
 	proxy_base.hpp
 	proxy_settings.hpp
 	puff.hpp
@@ -326,6 +329,7 @@ set(sources
 	disabled_disk_io.cpp
 	disk_buffer_holder.cpp
 	disk_buffer_pool.cpp
+	disk_cache.cpp
 	disk_completed_queue.cpp
 	disk_io_thread_pool.cpp
 	disk_job_fence.cpp
@@ -383,6 +387,8 @@ set(sources
 	posix_disk_io.cpp
 	posix_part_file.cpp
 	posix_storage.cpp
+	pread_disk_io.cpp
+	pread_storage.cpp
 	proxy_base.cpp
 	proxy_settings.cpp
 	puff.cpp

ChangeLog

@@ -1,5 +1,6 @@
 2.1.0 not released
 
+	* add a multi-threaded, pread()-based, disk I/O backend (pread_disk_io)
 	* try harder to bind TCP and UDP sockets to the same port
 	* made disk_interface's status_t type a flags type
 	* optimize resume data format to use less space

Jamfile

@@ -806,6 +806,7 @@ SOURCES =
 	directory
 	disk_buffer_holder
 	disk_buffer_pool
+	disk_cache
 	disk_completed_queue
 	disk_io_thread_pool
 	disabled_disk_io
@@ -910,6 +911,8 @@ SOURCES =
 	mmap
 	mmap_disk_io
 	mmap_storage
+	pread_disk_io
+	pread_storage
 	posix_disk_io
 	posix_part_file
 	posix_storage

Makefile

@@ -323,6 +323,7 @@ SOURCES = \
   disabled_disk_io.cpp            \
   disk_buffer_holder.cpp          \
   disk_buffer_pool.cpp            \
+  disk_cache.cpp                  \
   disk_completed_queue.cpp        \
   disk_io_thread_pool.cpp         \
   disk_job_fence.cpp              \
@@ -381,6 +382,8 @@ SOURCES = \
   posix_disk_io.cpp               \
   posix_part_file.cpp             \
   posix_storage.cpp               \
+  pread_disk_io.cpp               \
+  pread_storage.cpp               \
   proxy_base.cpp                  \
   proxy_settings.cpp              \
   puff.cpp                        \
@@ -497,6 +500,7 @@ HEADERS = \
   piece_block.hpp              \
   portmap.hpp                  \
   posix_disk_io.hpp            \
+  pread_disk_io.hpp            \
   read_resume_data.hpp         \
   session.hpp                  \
   session_handle.hpp           \
@@ -561,6 +565,8 @@ HEADERS = \
   aux_/disable_warnings_pop.hpp     \
   aux_/disable_warnings_push.hpp    \
   aux_/disk_buffer_pool.hpp         \
+  aux_/disk_cache.hpp               \
+  aux_/visit_block_iovecs.hpp       \
   aux_/disk_completed_queue.hpp     \
   aux_/disk_io_thread_pool.hpp      \
   aux_/disk_job_fence.hpp           \
@@ -627,6 +633,8 @@ HEADERS = \
   aux_/portmap.hpp                  \
   aux_/posix_part_file.hpp          \
   aux_/posix_storage.hpp            \
+  aux_/pread_disk_job.hpp           \
+  aux_/pread_storage.hpp            \
   aux_/proxy_base.hpp               \
   aux_/proxy_settings.hpp           \
   aux_/puff.hpp                     \
@@ -892,6 +900,8 @@ TEST_SOURCES = \
   test_dht.cpp \
   test_dht_storage.cpp \
   test_direct_dht.cpp \
+  test_disk_cache.cpp \
+  test_disk_io.cpp \
   test_dos_blocker.cpp \
   test_ed25519.cpp \
   test_enum_net.cpp \

bindings/python/src/session.cpp

@@ -30,6 +30,7 @@
 
 #include <libtorrent/mmap_disk_io.hpp>
 #include <libtorrent/posix_disk_io.hpp>
+#include <libtorrent/pread_disk_io.hpp>
 
 namespace boost
 {
@@ -882,6 +883,8 @@ namespace
 #endif
         if (disk_io == "posix_disk_io_constructor")
             s.disk_io_constructor = &lt::posix_disk_io_constructor;
+        else if (disk_io == "pread_disk_io_constructor")
+            s.disk_io_constructor = &lt::pread_disk_io_constructor;
         else
             s.disk_io_constructor = &lt::default_disk_io_constructor;
     }

examples/client_test.cpp

@@ -56,6 +56,7 @@ see LICENSE file.
 
 #include "libtorrent/mmap_disk_io.hpp"
 #include "libtorrent/posix_disk_io.hpp"
+#include "libtorrent/pread_disk_io.hpp"
 #include "libtorrent/disabled_disk_io.hpp"
 
 #include "torrent_view.hpp"
@@ -1347,7 +1348,7 @@ CLIENT OPTIONS
   -O                    print session stats counters to the log
   -1                    exit on first torrent completing (useful for benchmarks)
   -i <disk-io>          specify which disk I/O back-end to use. One of:
-                        mmap, posix, disabled
+                        mmap, posix, pread, disabled
 )"
 #ifdef TORRENT_UTP_LOG_ENABLE
 R"(
@@ -1561,6 +1562,10 @@ int main(int argc, char* argv[])
 #endif
 				if (arg == "posix"_sv)
 					params.disk_io_constructor = lt::posix_disk_io_constructor;
+#if TORRENT_HAVE_PREAD || defined TORRENT_WINDOWS
+				else if (arg == "pread"_sv)
+					params.disk_io_constructor = lt::pread_disk_io_constructor;
+#endif
 				else if (arg == "disabled"_sv)
 					params.disk_io_constructor = lt::disabled_disk_io_constructor;
 				else

include/libtorrent/aux_/debug_disk_thread.hpp

@@ -24,6 +24,7 @@ see LICENSE file.
 #include <string>
 #include <sstream>
 #include <unordered_map>
+#include <thread>
 
 #include "libtorrent/aux_/disk_job.hpp"
 #include "libtorrent/disk_interface.hpp"
@@ -81,18 +82,22 @@ inline std::string print_job(aux::disk_job const& j)
 		}
 
 		void operator()(job::file_priority const& j) const {
-			m_ss << "file-priority( num-files:" << j.prio.size() << " )";
+			m_ss << "file-priority( num-files: " << j.prio.size() << " )";
 		}
 
 		void operator()(job::clear_piece const& j) const {
-			m_ss << "clear-piece( piece:" << j.piece << " )";
+			m_ss << "clear-piece( piece: " << j.piece << " )";
 		}
 
 		void operator()(job::partial_read const& j) const {
 			m_ss << "partial-read( piece: " << j.piece << " offset: " << j.offset
 				<< " buf-offset: " << j.buffer_offset << " size: " << j.buffer_size << " )";
 		}
 
+		void operator()(job::kick_hasher const& j) const {
+			m_ss << "kick-hasher( piece: " << j.piece << " )";
+		}
+
 	private:
 		std::stringstream& m_ss;
 	};

include/libtorrent/aux_/disk_buffer_pool.hpp

@@ -21,6 +21,7 @@ see LICENSE file.
 #include <mutex>
 #include <functional>
 #include <memory>
+#include <optional>
 
 #include "libtorrent/io_context.hpp"
 #include "libtorrent/span.hpp"
@@ -54,6 +55,8 @@ namespace aux {
 			return m_in_use;
 		}
 
+		std::optional<int> flush_request() const;
+
 		void set_settings(settings_interface const& sett);
 
 	private:
@@ -67,10 +70,10 @@ namespace aux {
 		// cache size limit
 		int m_max_use;
 
-		// if we have exceeded the limit, we won't start
-		// allowing allocations again until we drop below
-		// this low watermark
+		// if we have exceeded the high watermark we start flushing blocks to
+		// disk until we're below the low watermark.
 		int m_low_watermark;
+		int m_high_watermark;
 
 		// if we exceed the max number of buffers, we start
 		// adding up callbacks to this queue. Once the number