General/TheLeaksTool (/usr/bin/leaks) is a UNIX tool that can help uncover memory leaks in your unix process. Leaks works best when malloc’s stack logging is activated via the General/MallocStackLogging shell variable (set the General/MallocHelp environment variable and run some command-line tool).

---

General/TheLeaksTool in Tiger shows a hex dump of whatever it thinks is leaking. Neat!

---

Can someone give a more elaborate description and example for someone who thinks (although brought up with a PDP-11), the terminal is evil ?

---

Here’s an example of how it works. First, we create a program that leaks a string:

#import <Foundation/Foundation.h>

#include

int main(int argc, char **argv) { General/NSString *s = General/[[NSString alloc] initWithString:@”I am a happy leak”]; s = nil; // leaked! General/NSLog(@”Looping, pid is %d”, getpid()); while(1) sleep(1); return 0; }

Now, we run it with malloc stack logging:

Hope:~/shell mikeash$ General/MallocStackLogging=1 ./leak (10494) malloc: recording stacks using standard recorder 2005-05-06 11:16:43.103 leak[10494] Looping, pid is 10494

In another shell, we run leaks on the process:

Hope:~ mikeash$ leaks 10494 Process 10494: 477 nodes malloced for 81 KB Process 10494: 2 leaks for 80 total leaked bytes. Leak: 0x00503d50 size=48 0x00490020 0x0061006d 0x00200061 0x00200068 .I. .a.m. .a. .h 0x00610070 0x00700079 0x0020006c 0x00650061 .a.p.p.y. .l.e.a 0x006b0000 0x00000000 0x00000000 0x00000000 .k………….. Call stack: [thread 2437]: | 0x0 | start | _start | main | -General/[NSPlaceholderString initWithString:] Leak: 0x00503de0 size=32 string ‘?rvt’ Call stack: [thread 2437]: | 0x0 | start | _start | main | -General/[NSPlaceholderString initWithString:] | General/CFStringCreateWithCharactersNoCopy | __CFStringCreateImmutableFunnel3 | _CFRuntimeCreateInstance | General/CFAllocatorAllocate

In the output, we find exactly what leaked, its contents, and where it was allocated. We also found another string which the frameworks leaked; hopefully it’s a one-time leak.

If you’re sure you only have one process with a particular name, you can also just do leaks “AppName”

Hmmm … I don’t seem to be getting the ASCII output bit in the terminal for strings!?!

are you using Tiger? did you do an upgrade install? do you have the latest dev tools?

---

Tiger is much more leakproof than earlier versions, which would always gush out strange objects I had nothing to do with. I’m seeing that magical ‘0 leaks for 0 total leaked bytes’ a lot more often now :)

---

Thanks a lot for these tips. With General/MallocStackLogging, I can now find the leaks, too! I fixed lots of leaks yesterday in one of my apps, I didn’t think it was possible to find so much coding errors without some kind of intelligence.. :-)