Re: Strange Memory Patterns

Jonathan Taylor

This sounds very similar to problems I have encountered myself.

Issue 1: GCD callbacks are part of an autorelease pool, but you can't rely on it getting drained in a reliable manner, so wrap your callbacks with your own explicit pool.

Issue 2: Background apps do not seem to always have their main thread autorelease pools drained reliably. A snippet of code I've posted a few times over the years:

// Create a periodic timer that "tickles" the main event loop to drain autorelease pools.
// Response from cocoa-dev discussion was that:
//  This is a long-standing problem with AppKit. According to the documentation,
//  "The Application Kit creates an autorelease pool on the main thread at the
//  beginning of every cycle of the event loop, and drains it at the end, thereby
//  releasing any autoreleased objects generated while processing an event."
//  However, this is somewhat misleading. The "end" of the event loop cycle is
//   immediately before the beginning. Thus, for example, if your app is in the background
//   and not receiving events, then the autorelease pool will not be drained. That's why
//   your memory drops significantly when you click the mouse or switch applications.
[JDispatchTimer allocRepeatingTimerOnQueue:dispatch_get_main_queue() atInterval:5.0 withHandler:^{
NSEvent *event = [NSEvent otherEventWithType:NSApplicationDefined location:NSZeroPoint modifierFlags:0 timestamp:[NSDate timeIntervalSinceReferenceDatewindowNumber:0 context:nil subtype:0 data1:0 data2:0];
[NSApp postEvent:event atStart:YES];

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