[Expander] leaves zombie threads running when toggling Show contents on a heavy zip file

[diver]

This is hrev44240, gcc2hybrid in vbox.

Toggling Show contents checkbox in Expander on a heavy zip file sometimes leads to a zombie threads which only visible in ProcessController.

bt 307
stack trace for thread 307 "ExpanderThread"
    kernel stack: 0x80676000 to 0x8067a000
      user stack: 0x7817a000 to 0x781ba000
frame               caller     <image>:function + offset
 0 80679cd0 (+  96) 8008a252   <kernel_x86> simple_reschedule() + 0x0482
 1 80679d30 (+  48) 80125978   <kernel_x86> hardware_interrupt(iframe*: 0x80679d6c) + 0x00e8
 2 80679d60 (+  12) 8012a5bd   <kernel_x86>:int_bottom + 0x003d
kernel iframe at 0x80679d6c (end = 0x80679dbc)
 eax 0x1            ebx 0x6fff0000      ecx 0x0          edx 0x8019a3ec
 esi 0x0            edi 0x820b2bcc      ebp 0x80679df4   esp 0x80679da0
 eip 0x800877b6  eflags 0x13202
 vector: 0xfb, error code: 0x0
 3 80679d6c (+ 136) 800877b6   <kernel_x86>:_mutex_unlock + 0x0122
 4 80679df4 (+ 272) 80068679   <kernel_x86>:handle_signals + 0x0cc5
 5 80679f04 (+  64) 8007c829   <kernel_x86>:thread_at_kernel_exit + 0x0015
 6 80679f44 (+ 100) 8012a965   <kernel_x86>:kernel_exit_handle_signals + 0x0006
user iframe at 0x80679fa8 (end = 0x8067a000)
 eax 0x8000000a     ebx 0x7d9774        ecx 0x1          edx 0x8019a3ec
 esi 0x32           edi 0x18002efc      ebp 0x781b9cdc   esp 0x80679fdc
 eip 0xffff0112  eflags 0x13216    user esp 0x781b9cc0
 vector: 0x63, error code: 0x0
 7 80679fa8 (+   0) ffff0112   <commpage>:commpage_syscall + 0x0002
 8 781b9cdc (+  32) 007abed3   <libroot.so> BPrivate<0x18002efc>::hoardLock(0x7ef500) + 0x003b
 9 781b9cfc (+  80) 007afa92   <libroot.so> BPrivate::threadHeap<0x18002b64>::malloc(uint32: 0x20 (32)) + 0x0096
10 781b9d4c (+  48) 007b0791   <libroot.so>:malloc + 0x0151
11 781b9d7c (+  64) 003245ed   <libbe.so>:__Q28BPrivate11BTokenSpace + 0x0051
12 781b9dbc (+  48) 00325477   <libbe.so> BPrivate::BTokenSpace<0x51da60>::InitAfterFork(0x180191c0) + 0x0023
13 781b9dec (+  64) 00308dd2   <libbe.so>:FilterDeleter__FPv (nearest) + 0x006e
14 781b9e2c (+  32) 007a8fed   <libroot.so>:_Exit (nearest) + 0x00b5
15 781b9e4c (+  48) 007a9172   <libroot.so>:fork + 0x00be
16 781b9e7c (+  48) 00212e7d   <_APP_> ExpanderThread<0x180d6398>::PipeCommand(int32: 3, 0x180a78b0 �     ▒��     ▒H2     ▒", 0x180d63b4) + 0x00fd
17 781b9eac (+ 160) 0021254f   <_APP_> ExpanderThread<0x180d6398>::ThreadStartup(0x0) + 0x026f
18 781b9f4c (+  48) 0021325e   <_APP_> GenericThread<0x180d6398>::ThreadFunction(0x0) + 0x002a
19 781b9f7c (+  48) 0021342c   <_APP_> GenericThread<0x180d6398>::private_thread_function(NULL) + 0x0028
20 781b9fac (+  48) 00736703   <libroot.so>:_get_next_team_info (nearest) + 0x005f
21 781b9fdc (+   0) 781b9fec   6224:ExpanderThread_297_stack@0x7817a000 + 0x3ffec