StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>You should add the synchronized wrapper around your functions unlockDatabase and lockDatabase, as well as isDatabaseLocked - it's not always guaranteed that a store or retrieval of a variable is atomic. Of course, if you do you'll want to move your sleep outside of the synchronized block, otherwise you'll deadlock. This is essentially a spin lock - it's not the most efficient method.</p> <pre><code>- (FMDatabase *)lockedDatabase { do { @synchronized(self) { if (![self isDatabaseLocked]) { isDatabaseLocked = YES; return self.database; } } usleep(20); }while(true); // continue until we get a lock } </code></pre> <p>Do you make sure that you don't use the FMDatabase object after having called unlockDatabase? You might want to consider a handle pattern - create an object that wraps the FMDatabase object, and as long as it exists, holds a lock on the database. In init you claim the lock, and in dealloc, you can release that lock. Then your client code doesn't need to worry about calling the various locking/unlocking functions, and you won't accidentally screw up. Try using NSMutex instead of the @synchronized blocks, see <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Multithreading/ThreadSafety/ThreadSafety.html#//apple_ref/doc/uid/10000057i-CH8-SW16" rel="nofollow noreferrer">http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Multithreading/ThreadSafety/ThreadSafety.html#//apple_ref/doc/uid/10000057i-CH8-SW16</a></p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload