Save session data once on shutdown, before waiting for stopped announces

Write it after downloads stop, or after the loop if skipped; one error policy for saves.

src/control.cc

@@ -10,6 +10,7 @@
 #include <torrent/utils/directory_events.h>
 
 #include "core/dht_manager.h"
+#include "core/download_list.h"
 #include "core/http_queue.h"
 #include "core/manager.h"
 #include "core/view_manager.h"
@@ -152,6 +153,15 @@ Control::handle_shutdown() {
     m_core->shutdown(true);
   }
 
+  if (!m_shutdown_session_saved) {
+    // Transfers are stopped, so this is the final state; write it before the
+    // stopped announces can hold the shutdown. A shutdown hook may already
+    // have queued these resume builds.
+    m_core->download_list()->session_save();
+    session_thread::manager()->flush_shutdown_saves();
+    m_shutdown_session_saved = true;
+  }
+
   if (!m_task_shutdown_clear_requests.is_scheduled())
     torrent::this_thread::scheduler()->wait_for_ceil_seconds(&m_task_shutdown_clear_requests, 10s);
 

src/control.h

@@ -50,6 +50,7 @@ public:
   bool                is_shutdown_completed();
   bool                is_shutdown_received()        { return m_shutdown_received; }
   bool                is_shutdown_started()         { return m_shutdown_quick; }
+  bool                is_shutdown_session_saved()   { return m_shutdown_session_saved; }
 
   void                initialize();
   void                cleanup();
@@ -114,6 +115,7 @@ private:
 
   align_cacheline
 
+  bool                m_shutdown_session_saved{};
   std::atomic<bool>   m_shutdown_received{};
   std::atomic<bool>   m_shutdown_quick{};
 };

src/main.cc

@@ -489,7 +489,11 @@ main(int argc, char** argv) {
 
     torrent::system::Thread::self()->event_loop();
 
-    control->core()->download_list()->session_save();
+    // A quick shutdown with no tracker request pending leaves the loop before
+    // handle_shutdown() could save.
+    if (!control->is_shutdown_session_saved())
+      control->core()->download_list()->session_save();
+
     control->cleanup();
 
   } catch (torrent::internal_error& e) {

src/session/session_manager.cc

@@ -429,42 +429,62 @@ SessionManager::process_finished_saves() {
   if (!m_active)
     throw torrent::internal_error("SessionManager::process_finished_saves() called while not active.");
 
-  for (auto& request : m_finished_saves) {
+  for (auto& request : m_finished_saves)
-    try {
+    consume_finished_save_unsafe(request);
-      request.first.get();
-
-    } catch (torrent::storage_error& e) {
-      LT_LOG("error saving download : storage error :download:%p path:%s : %s", request.second.download, request.second.path.c_str(), e.what());
-
-      if (m_last_storage_error_message + std::chrono::minutes(5) > torrent::this_thread::cached_time()) {
-        m_ignored_storage_error_count++;
-        continue;
-      }
-
-      lt_log_print(torrent::LOG_ERRORS, "Storage errors saving session data for download: ignored:%u : %s", m_ignored_storage_error_count, e.what());
-
-      m_last_storage_error_message = torrent::this_thread::cached_time();
-      m_ignored_storage_error_count = 0;
-
-      continue;
-
-    } catch (torrent::internal_error& e) {
-      LT_LOG("error saving download : internal error : download:%p path:%s : %s", request.second.download, request.second.path.c_str(), e.what());
-      throw;
-
-    } catch (...) {
-      LT_LOG("error saving download : unknown error : download:%p path:%s", request.second.download, request.second.path.c_str());
-      throw;
-    }
-
-    LT_LOG("finished saving download : download:%p path:%s", request.second.download, request.second.path.c_str());
-  }
 
   m_finished_saves.clear();
 
   callback_save_request();
 }
 
+// Storage errors share a five-minute log limit and count what they suppress.
+// Callers hold m_mutex.
+void
+SessionManager::report_storage_error_unsafe(const std::string& what) {
+  if (m_last_storage_error_message + std::chrono::minutes(5) > torrent::this_thread::cached_time()) {
+    m_ignored_storage_error_count++;
+    return;
+  }
+
+  lt_log_print(torrent::LOG_ERRORS, "Storage errors saving session data for download: ignored:%u : %s", m_ignored_storage_error_count, what.c_str());
+
+  m_last_storage_error_message = torrent::this_thread::cached_time();
+  m_ignored_storage_error_count = 0;
+}
+
+// The one policy for a finished save, on the session thread and in shutdown
+// flushes: storage errors go to report_storage_error_unsafe(), internal and
+// unknown errors propagate. Callers hold m_mutex.
+void
+SessionManager::consume_finished_save_unsafe(ProcessingSave& request) {
+  try {
+    request.first.get();
+
+  } catch (torrent::storage_error& e) {
+    LT_LOG("error saving download : storage error :download:%p path:%s : %s", request.second.download, request.second.path.c_str(), e.what());
+    report_storage_error_unsafe(e.what());
+    return;
+
+  } catch (torrent::internal_error& e) {
+    LT_LOG("error saving download : internal error : download:%p path:%s : %s", request.second.download, request.second.path.c_str(), e.what());
+    throw;
+
+  } catch (...) {
+    LT_LOG("error saving download : unknown error : download:%p path:%s", request.second.download, request.second.path.c_str());
+    throw;
+  }
+
+  LT_LOG("finished saving download : download:%p path:%s", request.second.download, request.second.path.c_str());
+}
+
+void
+SessionManager::flush_shutdown_saves() {
+  assert(torrent::this_thread::thread() == torrent::main_thread::thread());
+  flush_all_pending_builds();
+  std::unique_lock<std::mutex> lock(m_mutex);
+  flush_all_and_wait_unsafe(lock);
+}
+
 void
 SessionManager::flush_all_and_wait_unsafe(std::unique_lock<std::mutex>& lock) {
   LT_LOG("flushing all pending saves", 0);
@@ -484,10 +504,17 @@ SessionManager::flush_all_and_wait_unsafe(std::unique_lock<std::mutex>& lock) {
     m_finished_condition.wait(lock);
 
   for (auto& request : m_finished_saves)
-    LT_LOG("finished saving download : download:%p path:%s", request.second.download, request.second.path.c_str());
+    consume_finished_save_unsafe(request);
 
   m_finished_saves.clear();
 
+  // Report and reset what was suppressed since the last error line. The count
+  // includes saves the session thread consumed while this flush waited.
+  if (m_ignored_storage_error_count != 0) {
+    lt_log_print(torrent::LOG_ERRORS, "Storage errors flushing session data: ignored:%u", m_ignored_storage_error_count);
+    m_ignored_storage_error_count = 0;
+  }
+
   LT_LOG("flushed all pending saves", 0);
 }
 

src/session/session_manager.h

@@ -79,6 +79,7 @@ protected:
   void                cleanup();
 
   void                flush_all_pending_builds();
+  void                flush_shutdown_saves();
 
 private:
   void                callback_pending_builds();
@@ -98,6 +99,9 @@ private:
 
   using ProcessingSave = std::pair<std::future<void>, SaveRequest>;
 
+  void                consume_finished_save_unsafe(ProcessingSave& request);
+  void                report_storage_error_unsafe(const std::string& what);
+
   torrent::system::Thread*     m_thread;
   torrent::system::callback_id m_callback_id;