[lldb-dev] breakpoints inside loops

Adrian McCarthy amccarth at google.com
Wed Jun 24 16:08:19 PDT 2015

I'm finding that when I set a breakpoint inside a small loop, the
breakpoint triggers only the first time.  For example, given this code:

#include <thread>
#include <chrono>

int main() {
  for (int i = 0; i < 10; ++i) {
  return 0;

If I set the breakpoint on the sleep_for call, it gets hit the first time.

(lldb) target create "a.exe"
Current executable set to 'a.exe' (i686).
(lldb) br set -l 6
Breakpoint 1: where = a.exe`main + 36 at hello.cpp:6, address = 0x00423044
(lldb) list
(lldb) process launch
Process 9892 launching
Process 9892 launched: 'D:\src\hello\a.exe' (i686)
(lldb) Process 9892 stopped
* thread #1: tid = 0x216c, 0x001c3044 a.exe`main + 36 at hello.cpp:6, stop
reason = breakpoint 1.1
    frame #0: 0x001c3044 a.exe`main + 36 at hello.cpp:6
   4    int main() {
   5      for (int i = 0; i < 10; ++i) {
-> 6        std::this_thread::sleep_for(std::chrono::milliseconds(10));
   7      }
   8      return 0;
   9    }
frame variable
(int) i = 0

So far, so good.  But now, if I try to continue, I'd expect the breakpoint
to be hit again, for the i = 1 iteration.  Instead:

(lldb) continue
Process 9892 resuming
(lldb) Process 9892 exited with status = 0 (0x00000000)

If I turn on various levels of locking, I see that the breakpoint hits, but
the ThreadList::ShouldStop test fails, so the process resumes again and
again until the loop terminates.

I've been trying to fix TestCreateAfterAttach.py on Windows, but a very
similar issue is blocking.

Is my expectation incorrect?  Is this problem specific to Windows?

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