Enabling Windows disk cache (and adding option to disable it) to prevent a relatively prevalent ERROR_INVALID_PARAMETER.

From my test only the write cache was the culprit, if this can be confirmed the read cache can be disabled by default if that has a benefit.

(Other systems are unchanged.)

src/preferences/advancedsettings.h

@@ -13,7 +13,7 @@
 #include "preferences.h"
 
 enum AdvSettingsCols {PROPERTY, VALUE};
-enum AdvSettingsRows {DISK_CACHE, OUTGOING_PORT_MIN, OUTGOING_PORT_MAX, IGNORE_LIMIT_LAN, RECHECK_COMPLETED, LIST_REFRESH, RESOLVE_COUNTRIES, RESOLVE_HOSTS, MAX_HALF_OPEN, SUPER_SEEDING, NETWORK_IFACE, NETWORK_ADDRESS, PROGRAM_NOTIFICATIONS, TRACKER_STATUS, TRACKER_PORT,
+enum AdvSettingsRows {DISK_CACHE, OS_WRITE_CACHE, OS_READ_CACHE, OUTGOING_PORT_MIN, OUTGOING_PORT_MAX, IGNORE_LIMIT_LAN, RECHECK_COMPLETED, LIST_REFRESH, RESOLVE_COUNTRIES, RESOLVE_HOSTS, MAX_HALF_OPEN, SUPER_SEEDING, NETWORK_IFACE, NETWORK_ADDRESS, PROGRAM_NOTIFICATIONS, TRACKER_STATUS, TRACKER_PORT,
                     #if defined(Q_WS_WIN) || defined(Q_WS_MAC)
                       UPDATE_CHECK,
                     #endif
@@ -29,7 +29,7 @@ class AdvancedSettings: public QTableWidget {
 
 private:
   QSpinBox spin_cache, outgoing_ports_min, outgoing_ports_max, spin_list_refresh, spin_maxhalfopen, spin_tracker_port;
-  QCheckBox cb_ignore_limits_lan, cb_recheck_completed, cb_resolve_countries, cb_resolve_hosts,
+  QCheckBox cb_write_cache, cb_read_cache, cb_ignore_limits_lan, cb_recheck_completed, cb_resolve_countries, cb_resolve_hosts,
   cb_super_seeding, cb_program_notifications, cb_tracker_status, cb_confirm_torrent_deletion,
   cb_enable_tracker_ext;
   QComboBox combo_iface;
@@ -67,6 +67,8 @@ public slots:
     Preferences pref;
     // Disk write cache
     pref.setDiskCacheSize(spin_cache.value());
+    pref.disableOSWriteCache(cb_write_cache.isChecked());
+    pref.disableOSReadCache(cb_read_cache.isChecked());
     // Outgoing ports
     pref.setOutgoingPortsMin(outgoing_ports_min.value());
     pref.setOutgoingPortsMax(outgoing_ports_max.value());
@@ -159,6 +161,12 @@ private slots:
     spin_cache.setValue(pref.diskCacheSize());
     spin_cache.setSuffix(tr(" MiB"));
     setRow(DISK_CACHE, tr("Disk write cache size"), &spin_cache);
+    // OS write cache
+    cb_write_cache.setChecked(pref.disableOSWriteCache());
+    setRow(OS_WRITE_CACHE, tr("Disable OS caching of disk writes"), &cb_write_cache);
+    // OS read cache
+    cb_read_cache.setChecked(pref.disableOSReadCache());
+    setRow(OS_READ_CACHE, tr("Disable OS caching of disk reads"), &cb_read_cache);
     // Outgoing port Min
     outgoing_ports_min.setMinimum(0);
     outgoing_ports_min.setMaximum(65535);

src/preferences/preferences.h

@@ -934,6 +934,22 @@ public:
     setValue(QString::fromUtf8("Preferences/Downloads/DiskCache"), size);
   }
 
+  bool disableOSWriteCache() const {
+    return value(QString::fromUtf8("Preferences/Advanced/DisableOSWriteCache"), false).toBool();
+  }
+
+  void disableOSWriteCache(bool disable) {
+    setValue(QString::fromUtf8("Preferences/Advanced/DisableOSWriteCache"), disable);
+  }
+
+  bool disableOSReadCache() const {
+    return value(QString::fromUtf8("Preferences/Advanced/DisableOSReadCache"), false).toBool();
+  }
+
+  void disableOSReadCache(bool disable) {
+    setValue(QString::fromUtf8("Preferences/Advanced/DisableOSReadCache"), disable);
+  }
+
   uint outgoingPortsMin() const {
     return value(QString::fromUtf8("Preferences/Advanced/OutgoingPortsMin"), 0).toUInt();
   }

src/qtlibtorrent/qbtsession.cpp

@@ -404,12 +404,9 @@ void QBtSession::configureSession() {
   sessionSettings.auto_scrape_min_interval = 900; // 15 minutes
   sessionSettings.cache_size = pref.diskCacheSize()*64;
   qDebug() << "Using a disk cache size of" << pref.diskCacheSize() << "MiB";
-  // Disable OS cache to avoid memory problems (uTorrent behavior)
-#ifdef Q_WS_WIN
-  // Fixes huge memory usage on Windows 7 (especially when checking files)
-  sessionSettings.disk_io_write_mode = session_settings::disable_os_cache;
-  sessionSettings.disk_io_read_mode = session_settings::disable_os_cache;
-#endif
+  // Disabling the OS disk cache is intended to reduce memory usage (especially when checking files) but might be unreliable
+  sessionSettings.disk_io_write_mode = pref.disableOSWriteCache() ? session_settings::disable_os_cache : session_settings::enable_os_cache;
+  sessionSettings.disk_io_read_mode = pref.disableOSReadCache() ? session_settings::disable_os_cache : session_settings::enable_os_cache;
 #if LIBTORRENT_VERSION_MINOR > 15
   sessionSettings.anonymous_mode = pref.isAnonymousModeEnabled();
   if (sessionSettings.anonymous_mode) {