Shared Libraries and Thread Creation

Craig A. Vanderborgh craigv@voxware.com
Thu Dec 8 23:05:00 GMT 2005


Hello Everyone:

I am doing some research on using shared libraries w/GCJ 4.1 on x86, 
RHEL 4 (kernel 2.6.9-5.EL, uniprocessor)

I am seeing memory use patterns in top/ps from my test programs that I 
simply do not understand.  It seems that if I have a dynamically linked 
GCJ program (w/libgcj.so, libc.so, libstdc++.so) the cost of thread 
creation in terms of memory use is MUCH, MUCH higher than the same 
program statically linked.

As one example, consider my lovely "PauseWorld" program:

class PauseWorld {
  public static void main(String[] args) {
    System.out.println("Pause World from GCJ!");
    try {
      Thread.sleep(1000000000);
    } catch (Exception e) {
    }
  }
}

If this program is statically linked, its process when run has a 12180M 
VSZ, and a 3536 RSS.  When everything else is the same and the program 
is linked with shared libraries, it has a 23840 VSZ and a 6592 RSS.

When viewed via strace, the "clone" call for the static case looks like 
this:

clone(child_stack=0x84d5b88, 
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND) = 1544

versus the dynamically-linked case:

clone(child_stack=0x19c84c8, 
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
parent_tidptr=0x19c8bf8, {entry_number:6, base_addr:0x19c8bb0, 
limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, 
limit_in_pages:1, seg_not_present:0, useable:1}, child_tidptr=0x19c8bf8) 
= 21035

Why on earth would thread creation in the dynamically linked case 
consume so much more system memory (VSZ)??  Or does it?  Are the numbers 
being reported via top/ps misleading for some reason I do not understand?

Why would the dynamically linked version of this puny test require twice 
as much memory to run dynamically linked as it does statically?  And 
note - I have been able to observe (with the help of gdb) that it is THE 
ACT OF THREAD CREATION with the dynamically linked test program that 
causes the memory use to skyrocket!

Please advise.

Thanks in advance,
craig vanderborgh
voxware incorporated



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