Clear read_fd_set if EINTR received

[emrekultursay]

Summary

Leaving bits uncleared set causes callbacks to be triggered even
though there are no events to process. Starting with D131160
we have a callback that makes blocking read calls over pipe which
was causing the lldb-server main loop to become unresponsive / blocked
on Android.

[emrekultursay]

Fix indentation.

[labath]

Nice catch.

As discussed internally, it would be great if we could remove this android-specific code path (by removing support for OS versions which necessitated it).

[emrekultursay]

As discussed internally, it would be great if we could remove this android-specific code path (by removing support for OS versions which necessitated it).

For now, Android Studio still requires the ability to debug API levels 16-19. The next time that min API level is bumped up, we can revisit this.

[emrekultursay]

Can you submit the change for me?

[finagolfin]

@emrekultursay, do you think you can get this into the release/16.x branch next? It fixed lldb for us on the Android Termux app.

[emrekultursay]

Sure, you are right that it should be pulled back into release/16.x, and I expect it to apply cleanly. However, I don't know what mechanism should bve used to create cherry-pick changes into release branches on GitHub: (1) this was not a GitHub issue/PR, so I guess I cannot use that mechanism; (2) I can run git cherry-pick myself, and then run arc diff to create a new Phabricator review (with a new D number?) but I don't know if that's the right way, (3) maybe there's some special "arc" commands to create a cherry-pick? (4) any other way?

[finagolfin]

I looked online and it appears that you nominate a trunk commit by opening a github issue? I am new to this LLVM workflow myself, but here is what appears to be a recent example.

[labath]

Yes, that is the correct process.

lldb/source/Host/posix/MainLoopPosix.cpp

Status MainLoopPosix::RunImpl::Poll() {
   memset(&kernel_sigset, 0, sizeof(kernel_sigset));
   kernel_sigset.set = get_sigmask();
 
   struct {
     void *sigset_ptr;
     size_t sigset_len;
   } extra_data = {&kernel_sigset, sizeof(kernel_sigset)};
   if (syscall(__NR_pselect6, nfds, &read_fd_set, nullptr, nullptr, nullptr,
-              &extra_data) == -1 &&
-      errno != EINTR)
+              &extra_data) == -1) {
+    if (errno != EINTR)
       return Status(errno, eErrorTypePOSIX);
+    else
+      FD_ZERO(&read_fd_set);
+  }
 
   return Status();
 }
 #else
 Status MainLoopPosix::RunImpl::Poll() {
   read_fds.clear();
 
   sigset_t sigmask = get_sigmask();