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lambda_scheme [2013/09/22 02:22]
troyane [Todays approach to database access in Mixxx]
lambda_scheme [2013/09/22 05:21]
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 ===== Dia ===== ===== Dia =====
 +All of written above can be described by next sequence diagram
 {{ :​wiki:​callasync.png?​direct&​300 |}} {{ :​wiki:​callasync.png?​direct&​300 |}}
 +**NOTE:** Here is mistake -- we use ''​Qt::​QueuedConnection''​ (or ''​MainExecuter''​) instead of ''​Qt::​BlockingQueuedConnection''​.
 +===== Long transactions =====
 +Example of "​long"​ transaction is ''​LibraryScanner''​.
 +We already have working scheme on pausing library scanner (here we can make pause by clicking "​pause"​ button in respective ''​LibraryScannerDlg''​).
 +Main idea is to use same interface for accessing database -- ''​callSync''​.
 +Here uses cashing system -- we collect 50 tracks and wrap into one transaction. While that transaction is pending, user can be able to interact with Mixxx UI, for example, create playlists (even without need to click "​pause"​ button).
 +====== Idea of usage scheme based on chunks ======
 +''​LibraryScanner''​ runs in separate thred. ​
 +We already have ''​callSync''​ function, which calls synchronously. ​
 +Also there is mechanism that controls weather we are in ''​Main''​ thread or 
 +in other thread. In case of other thread we just sleep (sleep thread in background).
 +So, new API for long transaction expects possibility to divide all database
 +access into several **chunks** and send it one by one and wait until it
 +This synchronous scheme gives us great programming experience -- we avoid 
 +need of thread synchronization (and lot of inherited overhead codding). ​
 +Every thread just do ''​callSync''​ with adequate //(I mean, not so big, and not
 +so small)// transaction. Our scheme will be workable on lots of //​parallel// ​
 +working threads, and user input will be smooth as well.
 +All bad moments of this scheme is in that fact that ''​LibraryScanner''​ (or other "​long"​ transactions) ​
 +will cost more time and that in general case -- since we need to open lot 
 +of transactions. //(But we are talking about operations in separate thread, ​
 +so it can take its time).//
 +If it would be very important - we can rewrite scheme further. ​
 +But as I feel, now this is best solution -- chopped transactions.
lambda_scheme.txt ยท Last modified: 2013/09/22 05:21 by troyane