What is a Bad Alloc?
A bad alloc error is an error that comes up when X-Plane runs out of memory. This can happen for two reasons:
- We have run out of address space - that is, there is no more virtual memory left, or
- We have run out of page file/physical memory - that is, we can't back that virtual memory.
X-Plane can run out of memory for many reasons - everything that runs in the sim uses memory, and the amount used depends on what area you are in, what rendering settings you pick, and what third party add-ons you use. While I'd like to someday reach a point when the sim tells you gracefully that it's out of memory, it will always be a fact of life that at some point (hopefully an absurdly high one) the amount of stuff you've asked X-Plane to do will exceed how much memory you have.
(If you are thinking 64 bits, well, that will just change the problem from a crash to a grinding halt when we run out of physical memory.)
We see bad allocs when there are too many third party add-ons installed (XSquawkBox is a particular pig because it loads every CSL on startup), too complex scenery, and it can also be caused by drivers not efficiently using memory. (This is particularly a problem on Vista RTM.)
When X-Plane creates a curved airport taxiway, it allocates a temporary memory buffer to hold the intermediate product of the pavement. The size of that buffer depends on the complexity of the curve it is processing and a constant, based on the maximum curve smoothness.
In 920 I provided an option to crank up the curve smoothness in X-Plane. In the process, I increased that constant factor by 4x, which causes X-Plane to hit its memory ceiling on layouts that used to be acceptable. You'll see this problem more often on:
- Bigger, more complex layouts.
- Configurations that were already chewing up a lot of memory.
- Machines with less address space (Windows without /3GB, older Mac OS X operating systems.)
What To Do
The bad news is that we can't do an RC5 - we're out of time. But - there will be a patch - relatively soon. This bug is on the short list for a patch to fix 920.
In the meantime, there is actually a work-around. By coincidence, some of the internal rendering engine constants are viewable via the "private dataref" system -- basically a series of datarefs in the sim/private/... domain that I use for on-the-fly debugging. The dataref that matters here is:
If you load up DataRef Editor you'll see it has a value of 12 . That's too high. Changing it to 10 will allow otherwise problematic airports to load.
I will try to post a plugin in the next 10 days that sets this dataref to 10 on startup, effectively patching the problem. This will also limit the maximum smoothness of curves - but my guess is that if you see the crash (not all users do) then you can't run on the max airport curve setting anyway.
Of course the next patch will contain a real solution: a more efficient memory allocation scheme!