Multiple-instance support: open multiple instance, one instance update can directly reflect on another instance

[evan0greenup]

Currently, only single instance can be opened.

It would be nice to make notes support multiple instance toward single database be opened simultaneously, because user may edit different pages within a single database.

And the content change in one instance can immediately take effect on another instance.

implementation

avoid data corruption:

• Use transaction feature of underlying database (SQLite).
• Use filelock (OS-level)

Aware the content update when other instance make change:

• save the last update timestamp in a file. If the time is newer than the in-memory record, synchronize the content.
• use file-watcher to keep track of file update.

[zjeffer]

Instead of supporting multiple instances, I think it's better if we support one instance with multiple windows. It would accomplish what you propose without having to implement transactions/filelocks/synchronizations, as we would still handle the database through a single instance.

[nuttyartist]

What are you trying to accomplish, @evan0greenup? Editing the same note from multiple windows? If so, how about a split screen feature? Or tabs? Both features I've had on my mind.

[evan0greenup]

@zjeffer ,@nuttyartist , Here I explain the reasons why I make this proposal:

Previously, I make proposal on launch note with custom profile directory. #682. If launching the notes with different profile/database, It is supposed to run a different instance.

Comparison on two approach

The first one is what @nuttyartist and @zjeffer recommended. Attaching to existed instance with same profile/database. (This is also how firefox works). But it require programming with dbus, and the inter-process communication is quite complicated. At least, I have no clear idea on how to implement it. (May be because I am not experienced enough).

The second one is my proposal. Despite of whether there is existed instance running for given profile directory/database filename. Just to ensure in low level multiple instance toward single database will not cause corruption. This approach is straight-forward.

Cross-platform is a big factor for choosing one among these two approaches above.

[zjeffer]

The first one is what @nuttyartist and @zjeffer recommended. Attaching to existed instance with same profile/database. (This is also how firefox works). But it require programming with dbus, and the inter-process communication is quite complicated. At least, I have no clear idea on how to implement it. (May be because I am not experienced enough).

If you only need to accomplish editing multiple notes from the same database, you could add a way to open a note in a separate window (e.g. by double-clicking or with an option in the context menu), which would still be in the same process (so no IPC necessary).