labath added inline comments.
================
Comment at: lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp:1909
+ wait_status);
+ tid_events.try_emplace(thread_up->GetID(), wait_status);
+ }
----------------
mgorny wrote:
> Hmm, I'm a bit confused here. Why would the key already exist? I mean, you
> start with empty `tid_events` and catch only one event for every thread,
> correct?
It doesn't exist. It's just how the api is named. c++ std::map offers both
emplace and try_emplace (which, ironically, don't differ in "trying" -- they
only differ in the way they construct the pair). DenseMap offers only
try_emplace (maybe for that reason).
================
Comment at: lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp:1918
+ } else {
+ // This can happen if one of the events is an main thread exit.
+ LLDB_LOG(log, "... but the thread has disappeared");
----------------
mgorny wrote:
> Are we talking about some kind of race here? Or some thread that appears in
> `m_threads` but is not returned by `GetThreadByID()`?
>
> I was wondering if you could use thread pointers as keys.
The problem is when a thread disappears. This can happen in case of a main
thread exit or an execve, in which case we remove all non-main threads from the
list. However, we can still have some pending events for the other threads.
Now, I haven't managed to reproduce this in my experiments, but the manpage is
adamant that a SIGKILL should immediately terminate a process. In my (limited)
tests the debugger always got a PTRACE_EVENT_EXIT stop for each threads (which
is again something that the manpage says should not happen), so we
theoretically (with careful management of thread lifetimes) might ensure that a
thread with pending events does not disappear, but depending on it doesn't seem
like a good idea.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D116372/new/
https://reviews.llvm.org/D116372
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