added disk-checking delay, to leave room for other disk operations while checking a torrent

ChangeLog

@@ -1,3 +1,4 @@
+	* introduced a mechanism to be lighter on the disk when checking torrents
 	* applied temporary memory storage optimization to when checking
 	  a torrent as well
 	* removed hash_for_slot() from storage_interface. It is now implemented

docs/manual.rst

@@ -3441,6 +3441,8 @@ session_settings
 		int send_socket_buffer_size;
 
 		bool optimize_hashing_for_speed;
+
+		int file_checks_delay_per_block;
 	};
 
 ``user_agent`` this is the client identification to the tracker.
@@ -3817,6 +3819,12 @@ is false, a single block will be allocated (16 kB), and the unhashed parts
 of the piece are read, one at a time, and hashed in this single block. This
 is appropriate on systems that are memory constrained.
 
+``file_checks_delay_per_block`` is the number of milliseconds to sleep
+in between disk read operations when checking torrents. This defaults
+to 0, but can be set to higher numbers to slow down the rate at which
+data is read from the disk while checking. This may be useful for
+background tasks that doesn't matter if they take a bit longer, as long
+as they leave disk I/O time for other processes.
 
 pe_settings
 ===========

include/libtorrent/disk_io_thread.hpp

@@ -318,9 +318,12 @@ namespace libtorrent
 		mutable mutex_t m_queue_mutex;
 		boost::condition m_signal;
 		bool m_abort;
+		bool m_waiting_to_shutdown;
 		std::list<disk_io_job> m_jobs;
 		size_type m_queue_buffer_size;
 
+		ptime m_last_file_check;
+
 		// this protects the piece cache and related members
 		mutable mutex_t m_piece_mutex;
 		// write cache

include/libtorrent/session_settings.hpp

@@ -166,6 +166,7 @@ namespace libtorrent
 			, recv_socket_buffer_size(0)
 			, send_socket_buffer_size(0)
 			, optimize_hashing_for_speed(true)
+			, file_checks_delay_per_block(0)
 		{}
 
 		// this is the user agent that will be sent to the tracker
@@ -559,6 +560,16 @@ namespace libtorrent
 		// optimized for memory usage instead of the
 		// number of read operations
 		bool optimize_hashing_for_speed;
+
+		// if > 0, file checks will have a short
+		// delay between disk operations, to make it 
+		// less intrusive on the system as a whole
+		// blocking the disk. This delay is specified
+		// in milliseconds and the delay will be this
+		// long per 16kiB block
+		// the default of 10 ms/16kiB will limit
+		// the checking rate to 1.6 MiB per second
+		int file_checks_delay_per_block;
 	};
 
 #ifndef TORRENT_DISABLE_DHT

src/disk_io_thread.cpp

@@ -253,6 +253,7 @@ namespace libtorrent
 	disk_io_thread::disk_io_thread(asio::io_service& ios, int block_size)
 		: disk_buffer_pool(block_size)
 		, m_abort(false)
+		, m_waiting_to_shutdown(false)
 		, m_queue_buffer_size(0)
 		, m_ios(ios)
 		, m_work(io_service::work(m_ios))
@@ -272,6 +273,7 @@ namespace libtorrent
 	{
 		mutex_t::scoped_lock l(m_queue_mutex);
 		disk_io_job j;
+		m_waiting_to_shutdown = true;
 		j.action = disk_io_job::abort_thread;
 		m_jobs.insert(m_jobs.begin(), j);
 		m_signal.notify_all();
@@ -1217,7 +1219,7 @@ namespace libtorrent
 					mutex_t::scoped_lock jl(m_queue_mutex);
 
 					for (std::list<disk_io_job>::iterator i = m_jobs.begin();
-							i != m_jobs.end();)
+						i != m_jobs.end();)
 					{
 						if (i->action == disk_io_job::read)
 						{
@@ -1540,6 +1542,20 @@ namespace libtorrent
 					int piece_size = j.storage->info()->piece_length();
 					for (int processed = 0; processed < 4 * 1024 * 1024; processed += piece_size)
 					{
+						ptime now = time_now();
+						if (now - m_last_file_check < milliseconds(m_settings.file_checks_delay_per_block))
+						{
+							int sleep_time = m_settings.file_checks_delay_per_block
+								* (piece_size / (16 * 1024))
+								- total_milliseconds(now - m_last_file_check);
+	
+							boost::thread::sleep(boost::get_system_time()
+								+ boost::posix_time::milliseconds(sleep_time));
+						}
+						m_last_file_check = time_now();
+
+						if (m_waiting_to_shutdown) break;
+
 						ret = j.storage->check_files(j.piece, j.offset, j.str);
 
 #ifndef BOOST_NO_EXCEPTIONS

src/session.cpp

@@ -125,6 +125,11 @@ namespace libtorrent
 		set.use_parole_mode = false;
 		set.prioritize_partial_pieces = true;
 
+		// be extra nice on the hard drive when running
+		// on embedded devices. This might slow down
+		// torrent checking
+		set.file_checks_delay_per_block = 15;
+
 		// only have 4 files open at a time
 		set.file_pool_size = 4;
 

src/session_impl.cpp

@@ -639,6 +639,7 @@ namespace aux {
 		if (m_settings.cache_size != s.cache_size
 			|| m_settings.cache_expiry != s.cache_expiry
 			|| m_settings.optimize_hashing_for_speed != s.optimize_hashing_for_speed
+			|| m_settings.file_checks_delay_per_block != s.file_checks_delay_per_block
 #ifndef TORRENT_DISABLE_MLOCK
 			|| m_settings.lock_disk_cache != s.lock_disk_cache
 #endif