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Fix flake in TestZerothFrame.py (llvm#96685)
This test is currently flaky on a local Windows amd64 build. The reason is that it relies on the order of `process.threads` but this order is nondeterministic: If we print lldb's inputs and outputs while running, we can see that the breakpoints are always being set correctly, and always being hit: ```sh runCmd: breakpoint set -f "main.c" -l 2 output: Breakpoint 1: where = a.out`func_inner + 1 at main.c:2:9, address = 0x0000000140001001 runCmd: breakpoint set -f "main.c" -l 7 output: Breakpoint 2: where = a.out`main + 17 at main.c:7:5, address = 0x0000000140001021 runCmd: run output: Process 52328 launched: 'C:\workspace\llvm-project\llvm\build\lldb-test-build.noindex\functionalities\unwind\zeroth_frame\TestZerothFrame.test_dwarf\a.out' (x86_64) Process 52328 stopped * thread #1, stop reason = breakpoint 1.1 frame #0: 0x00007ff68f6b1001 a.out`func_inner at main.c:2:9 1 void func_inner() { -> 2 int a = 1; // Set breakpoint 1 here ^ 3 } 4 5 int main() { 6 func_inner(); 7 return 0; // Set breakpoint 2 here ``` However, sometimes the backtrace printed in this test shows that the process is stopped inside NtWaitForWorkViaWorkerFactory from `ntdll.dll`: ```sh Backtrace at the first breakpoint: frame #0: 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 frame #1: 0x00007ffecc74585e ntdll.dll`RtlClearThreadWorkOnBehalfTicket + 862 frame llvm#2: 0x00007ffecc3e257d kernel32.dll`BaseThreadInitThunk + 29 frame llvm#3: 0x00007ffecc76af28 ntdll.dll`RtlUserThreadStart + 40 ``` When this happens, the test fails with an assertion error that the stopped thread's zeroth frame's current line number does not match the expected line number. This is because the test is looking at the wrong thread: `process.threads[0]`. If we print the list of threads each time the test is run, we notice that threads are sometimes in a different order, within `process.threads`: ```sh Thread 0: thread llvm#4: tid = 0x9c38, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 Thread 1: thread llvm#2: tid = 0xa950, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 Thread 2: thread #1: tid = 0xab18, 0x00007ff64bc81001 a.out`func_inner at main.c:2:9, stop reason = breakpoint 1.1 Thread 3: thread llvm#3: tid = 0xc514, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 Thread 0: thread llvm#3: tid = 0x018c, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 Thread 1: thread #1: tid = 0x85c8, 0x00007ff7130c1001 a.out`func_inner at main.c:2:9, stop reason = breakpoint 1.1 Thread 2: thread llvm#2: tid = 0xf344, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 Thread 3: thread llvm#4: tid = 0x6a50, 0x00007ffecc7b3bf4 ntdll.dll`NtWaitForWorkViaWorkerFactory + 20 ``` Use `self.thread()` to consistently select the correct thread, instead. Co-authored-by: kendal <[email protected]>
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