add a workaround in GetLine to account for ReadFile not reporintg error

[lanza]

Summary

ReadFile on Windows is supposed to set ERROR_OPERATION_ABORTED according
to the docs on MSDN. However, this has evidently been a known bug since
Windows 8. Therefore, we can't detect if a signal interrupted in the
fgets. So pressing ctrl-c causes the repl to end and the process to
exit. A temporary workaround is just to attempt to fgets twice until
this bug is fixed.

A possible alternative would be to set a flag in the sigint_handler
and simply check that flag in the true part of the if statement.
However, signal handlers on Windows are asynchronous and this would
require sleeping on the repl loop thread while still not necessarily
guarnateeing that you caught the sigint.

[aleksandr.urakov]

I do not fully understand how this works... Does the second fgets sets error to EINTR?

[stella.stamenova]

LGTM!

[lanza]

@aleksandr.urakov Nope, there is no eintr on Windows. There's supposed to be a ERROR_OPERATION_ABORTED according to the MSDN docs, but it evidently is a known bug that it's not happening. So you can't catch that it failed. This change does nothing other than let the user hit ctrl+c twice before exiting since we can't test if ctrl+c was hit in any way (without sleeping on the real thread, that is). The normal signal handling is still done as always, but Windows handles it asynchronously independent of this.

What was happening was a user would press ctrl+c to interrupt and fgets would fail undetectably and so this chunk of code thought that the user was done and it caused lldb to exit. Meanwhile, the normal signal handling code would attempt to interrupt the process, but the repl ending meaning lldb exited.

[lanza]

Rebase

[aleksandr.urakov]

That makes sense, thank you!

source/Core/IOHandler.cpp

if (in) {
           }
         }
       }
       char buffer[256];
       bool done = false;
       bool got_line = false;
       m_editing = true;
       while (!done) {
+#ifdef _WIN32
+        // ReadFile on Windows is supposed to set ERROR_OPERATION_ABORTED
+        // according to the docs on MSDN. However, this has evidently been a
+        // known bug since Windows 8. Therefore, we can't detect if a signal
+        // interrupted in the fgets. So pressing ctrl-c causes the repl to end
+        // and the process to exit. A temporary workaround is just to attempt to
+        // fgets twice until this bug is fixed.
+        if (fgets(buffer, sizeof(buffer), in) == nullptr &&
+            fgets(buffer, sizeof(buffer), in) == nullptr) {
+#else
         if (fgets(buffer, sizeof(buffer), in) == nullptr) {
+#endif
           const int saved_errno = errno;
           if (feof(in))
             done = true;
           else if (ferror(in)) {
             if (saved_errno != EINTR)
               done = true;
           }
         } else {