[guitargeek]

IOHandler.cxx captured the stdout and stderr of C and C++ code in notebooks by redirecting the file descriptors into pipes, and ran notebook cells through TInterpreter, reporting C++ exceptions. Both are now Python: the capture with os.dup2() and pipes, the cell execution through gInterpreter, with cppyy translating C++ exceptions.

The capture used to read the pipes only after flushing C stdio, so a cell that wrote more than the pipe holds (64 kB on macOS) hung: the writer blocked on the full pipe holding the stream lock that the flush waited for. Now a thread per stream drains its pipe as long as the capture runs. A process started during the capture can keep a pipe open, so the end of a capture waits at most a second for the rest of the output.

Other differences:

• each IOHandler has its own capture, instead of all sharing one, which the first one to be deleted destroyed;
• deleting an IOHandler ends its capture;
• output that is not valid UTF-8 is decoded with replacement characters instead of raising;
• ProcessLine() and Declare() release the GIL (set in the facade), so the ROOT kernel streams output while a cell runs.

🤖 Done with the help of AI

[github-actions]

Test Results

    2 files      2 suites   4h 59m 35s ⏱️
2 635 tests 2 635 ✅ 0 💤 0 ❌
4 955 runs  4 955 ✅ 0 💤 0 ❌

Results for commit 3fecbbf.