Convert to CupsPrintJobManagerImpl to TaskScheduler.

chrome/browser/chromeos/printing/cups_print_job_manager_impl.h

Index: chrome/browser/chromeos/printing/cups_print_job_manager_impl.h
diff --git a/chrome/browser/chromeos/printing/cups_print_job_manager_impl.h b/chrome/browser/chromeos/printing/cups_print_job_manager_impl.h
index cdf723691dc5b914fc963c6fa435d7e120698592..101655a1aa1124edc0f5670865cfcd45658f17e2 100644
--- a/chrome/browser/chromeos/printing/cups_print_job_manager_impl.h
+++ b/chrome/browser/chromeos/printing/cups_print_job_manager_impl.h
@@ -11,7 +11,11 @@
 #include <unordered_map>
 #include <vector>
 
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/sequence_checker.h"
+#include "base/sequenced_task_runner.h"
+#include "base/single_thread_task_runner.h"
 #include "chrome/browser/chromeos/printing/cups_print_job.h"
 #include "chrome/browser/chromeos/printing/cups_print_job_manager.h"
 #include "chrome/browser/chromeos/printing/printers_manager.h"
@@ -32,6 +36,26 @@ struct QueryResult {
   std::vector<::printing::QueueStatus> queues;
 };
 
+// A wrapper around the CUPS connection to ensure that it's always accessed on
+// the same sequence.
+class CupsWrapper : public base::SupportsWeakPtr<CupsWrapper> {
+ public:
+  CupsWrapper();
+  ~CupsWrapper();
+
+  // Query CUPS for the current jobs for the given |printer_ids|.  Writes result
+  // to |result|.
+  void QueryCups(const std::vector<std::string>& printer_ids,
+                 QueryResult* result);
+
+  // Cancel the print job on the blocking thread.
+  void CancelJobImpl(const std::string& printer_id, const int job_id);
+
+ private:
+  ::printing::CupsConnection cups_connection_;
+  SEQUENCE_CHECKER(sequence_checker_);
+};

[gab, 2017/06/27 17:44:18]

DISALLOW_COPY_AND_ASSIGN

[skau, 2017/06/27 20:25:41]

Done.

+
 class CupsPrintJobManagerImpl : public CupsPrintJobManager,
                                 public content::NotificationObserver {
  public:
@@ -65,21 +89,12 @@ class CupsPrintJobManagerImpl : public CupsPrintJobManager,
   // to UpdateJobs.
   void PostQuery();
 
-  // Updates the state of a print job based on |printer_status| and |job|.
-  // Returns true if observers need to be notified of an update.
-  bool UpdatePrintJob(const ::printing::PrinterStatus& printer_status,
-                      const ::printing::CupsJob& job,
-                      CupsPrintJob* print_job);
-
   // Process jobs from CUPS and perform notifications.
-  void UpdateJobs(const QueryResult& results);
+  void UpdateJobs(std::unique_ptr<QueryResult> results);
 
   // Mark remaining jobs as errors and remove active jobs.
   void PurgeJobs();
 
-  // Cancel the print job on the blocking thread.
-  void CancelJobImpl(const std::string& printer_id, const int job_id);
-
   // Notify observers that a state update has occured for |job|.
   void NotifyJobStateUpdate(CupsPrintJob* job);
 
@@ -92,8 +107,12 @@ class CupsPrintJobManagerImpl : public CupsPrintJobManager,
   // Records the number of consecutive times the GetJobs query has failed.
   int retry_count_ = 0;
 
-  ::printing::CupsConnection cups_connection_;
+  CupsWrapper cups_wrapper_;

[gab, 2017/06/27 17:44:18]

To ensure this is deleted on its sequence you'll need to use the std::unique_ptr
+ base::OnTaskRunnerDeleter documented @
https://cs.chromium.org/chromium/src/base/sequenced_task_runner.h?rcl=e7e9085...

That way your usage of WeakPtrs will be safe. In fact, you won't need the
WeakPtrs at all as the deletion will always run after all tasks already posted
(and there won't be any tasks posted after per this instance being gone and
|query_runner_| no longer being accessible (other than through
SequencedTaskRunnerHandle::Get() on the sequence itself but tasks on
|query_runner_| don't post back to self so it's fine).

[skau, 2017/06/27 20:25:41]

Thanks!  I was looking for that.

   content::NotificationRegistrar registrar_;
+  // Task runner for queries to CUPS.
+  scoped_refptr<base::SequencedTaskRunner> query_runner_;
+  // Task runner to for the Browser UI thread.
+  scoped_refptr<base::SingleThreadTaskRunner> browser_thread_runner_;
   base::WeakPtrFactory<CupsPrintJobManagerImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CupsPrintJobManagerImpl);