AlexHarker

I'm working on a mac using OSAtomicSwapAnCompare32Barrier for some threadsafety issues.

This requires that the address it operates on is 32bit (4-btye) aligned. The variables I'm using are stored in my external object structure directly in one case, and in a struct inside my object structure in another case.

I assume the compiler will pad the structure so that (assuming a 4-byte aligned starting address) the variables will be 4-byte aligned. So far so go - this seemed to work.

However, I got one crash on calling this function today (in 4.63) with the error - bad/invalid address - which would seem to imply to me that the max object structure may not be 4-byte aligned, or that my assumption about the compiler is wrong - in which case I've been exceptionally lucky.

Anyone know what the situation is with this is in both 4.6 and 5? One solution would be to store pointers in my object structure to these variables and allocate/free them manually, and if I have to that's what I'll do, but it'd be good to figure out exactly what's going on here, and if there's another way round first, or if I've perhaps misdiagnosed the issue.

The first few lines of the crash report are below, just in case they are relevant.

Path: /Applications/MaxMSP 4.6/MaxMSP.app/Contents/MacOS/MaxMSP

Codes: KERN_INVALID_ADDRESS (0x0001) at 0x8000000f

0 <>     0xffff0084 __compare_and_swap32 + 4 (cpu_capabilities.h:207)

1 AHarker. hierarchy_multinode     0x16bf3cd6 multinode_make_node + 226 (HIerarchy Multinode.c:192)

This requires that the address it operates on is 32bit (4-btye) aligned. The variables I'm using are stored in my external object structure directly in one case, and in a struct inside my object structure in another case. 

I assume the compiler will pad the structure so that (assuming a 4-byte aligned starting address) the variables will be 4-byte aligned. So far so go - this seemed to work. 

Host Name:      Alex-Harkers-Computer
Date/Time:      2009-10-09 15:38:57.428 +0100
OS Version:     10.4.11 (Build 8S2167)
Report Version: 4

Command: MaxMSP
Path:    /Applications/MaxMSP 4.6/MaxMSP.app/Contents/MacOS/MaxMSP
Parent:  WindowServer [64]

Exception:  EXC_BAD_ACCESS (0x0001)
Codes:      KERN_INVALID_ADDRESS (0x0001) at 0x8000000f

Thread 0 Crashed:
0   <> 	0xffff0084 __compare_and_swap32 + 4 (cpu_capabilities.h:207)
1   AHarker. hierarchy_multinode   	0x16bf3cd6 multinode_make_node + 226 (HIerarchy Multinode.c:192)


Object struct alignment in Max 4.63 and 5