macOS Strange mmap error..

[gfroyle]

I have a C program that calls "calloc" to get clean memory and then frees it when no longer needed.

About 95% of the time, the program runs fine and seems to be correct.

About 5% of the time, it IMMEDIATELY crashes with the following error

malloc: *** mmap(size=3568361472) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug


I don't call malloc directly (though calloc calls malloc) and I certainly am never asking for 3.5Gb of space, so somehow the whole request seems to have gone awry.

If I simply run the program again, making no changes to anything, then it usually works the next time, so it appears to be a RANDOM and TRANSIENT error.

Nevertheless I would prefer to know why it is doing this, and how it can be stopped..

I am using

gcc (GCC) 4.2.2
Copyright (C) 2007 Free Software Foundation, Inc.

on an Intel Mac running MacOS X 10.5.5


Thanks

Gordon

 

[Guiyon]

What is the code snippit that's producing the error? That looks like a GIGO problem.

 

[Catfish_Man]

set a breakpoint in malloc_error_break and check your program state; perhaps you're calling calloc with an uninitialized variable in some edge case?

 

[gfroyle]

Aarghhh...

What is the code snippit that's producing the error? That looks like a GIGO problem.

Yes a GIGO error indeed... I had modified the program so that a variable that was previously read from the command line was instead part of each line of input.

But I had left in a stray line of code that attempted to USE the variable before any lines of input were processed... so it contained garbage. If it happened by luck to contain 0 then nothing bad happened, but otherwise crash...

I can't believe I could read my code 50 times and not spot this before making a fool of myself in public :-(

Oh well..

Gordon

 

[yeroen]

Y
I can't believe I could read my code 50 times and not spot this before making a fool of myself in public :-(

Oh well..

Gordon

Actually, it's refreshing to see a well-posed question on these boards for a change. Lately it's all been nothing but pleas for homework solutions and fractured-english non-questions like 'i want write operating system please to explain how xcode'

 

[Guiyon]

Yes a GIGO error indeed... I had modified the program so that a variable that was previously read from the command line was instead part of each line of input.

But I had left in a stray line of code that attempted to USE the variable before any lines of input were processed... so it contained garbage. If it happened by luck to contain 0 then nothing bad happened, but otherwise crash...

I can't believe I could read my code 50 times and not spot this before making a fool of myself in public :-(

Oh well..

Gordon

Heh, those are always the worst issues. I think I spend a good day or two one a chunk of code with a similar project; had an off-by-one error in a mod op which, in turn, caused my code to occasionally scribble all over one of my interpreter's core data structures. The problem was made even worse because I was running the code an ATMega microcontroller; at least with a standard OS you have some sort of memory protection...