erts: Make select message into a non-msg signal

[garazdawi]

Summary by Sourcery

Enhance the I/O event handling by converting select messages into non-message signals, improving the efficiency of the system. Update the internal documentation to include a detailed overview of the check I/O subsystem. Add new test cases to ensure the correct functionality of the scheduler polling mechanism for NIFs.

Enhancements:

• Convert select message into a non-message signal to improve efficiency in handling I/O events.

Documentation:

• Add a new internal documentation file 'CheckIO.md' that provides an overview of the check I/O subsystem, its components, and how it operates.

Tests:

• Introduce new test cases in 'nif_SUITE.erl' to verify the functionality of the scheduler polling for NIFs, including tests for socket pairs and scheduler pollset operations.

[garazdawi]

@sourcery-ai review

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request modifies the ERTS check I/O subsystem to optimize NIF select message handling by introducing a non-message signal mechanism and scheduler pollset optimizations. The changes aim to improve performance by reducing message copying and better handling of I/O events in scheduler pollsets.

Sequence diagram for NIF select message handling

sequenceDiagram
    participant NIF
    participant Scheduler
    participant Process
    participant IO

    NIF->>Scheduler: enif_select
    Scheduler->>IO: erts_io_handle_nif_select
    IO->>Scheduler: Return message
    Scheduler->>Process: Send signal
    Process->>Scheduler: Acknowledge signal
    Scheduler->>NIF: Signal processed

Loading

Class diagram for ERTS check I/O subsystem changes

classDiagram
    class ErtsNifSelectSignalData {
        Eterm message
        ErlNifEvent evt
    }

    class erts_nif_select_event {
        ErtsMessage* mp
        Eterm pid
    }

    class ErtsSchedulerData {
        ErtsSysFdType nif_select_fds[5]
    }

    class ErtsMessage {
        ErlHeapFragment hfrag
    }

    class ErlHeapFragment {
        size_t used_size
        size_t alloc_size
    }

    ErtsNifSelectSignalData --> erts_nif_select_event : used in
    erts_nif_select_event --> ErtsMessage : contains
    ErtsSchedulerData --> ErtsSysFdType : uses
    ErtsMessage --> ErlHeapFragment : contains
    ErlHeapFragment : used_size
    ErlHeapFragment : alloc_size
    ErtsSchedulerData : nif_select_fds[5]

Loading

File-Level Changes

Change	Details	Files
Introduce non-message signal mechanism for NIF select events	Add new ERTS_SIG_Q_OP_NIF_SELECT operation for handling NIF select events Implement signal handling infrastructure for NIF select events Add support for converting NIF select messages to signals Modify message creation to support extra space for signal data	erts/emulator/beam/erl_proc_sig_queue.c erts/emulator/beam/erl_proc_sig_queue.h erts/emulator/beam/erl_nif.c
Optimize scheduler pollset handling for NIF select events	Add NIF select state tracking in scheduler data structure Implement automatic migration of FDs to scheduler pollset after threshold Add cleanup mechanism for NIF select handles in scheduler Modify poll control logic to handle scheduler pollset operations	erts/emulator/sys/common/erl_check_io.c erts/emulator/beam/erl_process.h erts/emulator/beam/erl_process.c
Add comprehensive test coverage for scheduler pollset functionality	Add new select_scheduler test case Implement test utilities for scheduler pollset verification Add test cases for FD migration and cleanup Add test cases for parallel FD handling	erts/emulator/test/nif_SUITE.erl erts/emulator/test/nif_SUITE_data/nif_SUITE.c
Add documentation for Check I/O subsystem	Document polling mechanisms on Unix and Windows Explain Check I/O subsystem architecture Document NIF and Port interactions with Check I/O Add implementation details for different polling methods	erts/emulator/internal_doc/CheckIO.md

---

Tips and commands

Interacting with Sourcery

• Trigger a new review: Comment @sourcery-ai review on the pull request.
• Continue discussions: Reply directly to Sourcery's review comments.
• Generate a GitHub issue from a review comment: Ask Sourcery to create an
  issue from a review comment by replying to it.
• Generate a pull request title: Write @sourcery-ai anywhere in the pull
  request title to generate a title at any time.
• Generate a pull request summary: Write @sourcery-ai summary anywhere in
  the pull request body to generate a PR summary at any time. You can also use
  this command to specify where the summary should be inserted.

Customizing Your Experience

Access your dashboard to:

• Enable or disable review features such as the Sourcery-generated pull request
  summary, the reviewer's guide, and others.
• Change the review language.
• Add, remove or edit custom review instructions.
• Adjust other review settings.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.

[sourcery-ai]

Hey @garazdawi - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟡 General issues: 3 issues found
• 🟢 Security: all looks good
• 🟡 Testing: 1 issue found
• 🟡 Complexity: 1 issue found
• 🟢 Documentation: all looks good

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}

[sourcery-ai]

issue (testing): Test needed for ECONNRESET error condition in read_nif

A new test case should be added to verify that ECONNRESET is properly handled and returns atom_eof. This is an important edge case that should be explicitly tested.

[sourcery-ai]

issue (typo): Fix typo: 'readying' should be 'reading'

[sourcery-ai]

issue (typo): Fix typo: 'everything' should be 'everytime'

[sourcery-ai]

issue (typo): Correct the plural form of 'Unix'

The plural form should be 'Unixes' rather than 'Unix'es'

[sourcery-ai]

issue (complexity): Consider extracting helper functions for scheduler polling and NIF select handling logic

The scheduler polling and NIF select handling logic adds significant complexity through nested flag manipulation. Consider extracting helper functions to improve readability:

static ERTS_INLINE void
update_scheduler_state(ErtsDrvEventState *state, ErtsPollEvents pe, ErtsPollOp op) 
{
    if (state->flags & ERTS_EV_FLAG_SCHEDULER) {
        if (!(state->flags & ERTS_EV_FLAG_IN_SCHEDULER))
            op = ERTS_POLL_OP_ADD;
        ErtsPollEvents res = erts_poll_control(get_scheduler_pollset(), 
            state->fd, op, pe & ERTS_POLL_EV_IN, NULL);
        if (op == ERTS_POLL_OP_ADD && res & ERTS_POLL_EV_IN)
            state->flags |= ERTS_EV_FLAG_IN_SCHEDULER;
        else if (op == ERTS_POLL_OP_DEL)
            state->flags &= ~ERTS_EV_FLAG_IN_SCHEDULER;
    }
}

This would simplify erts_io_control_wakeup() by encapsulating the scheduler state transitions. Similar helper functions could be extracted for NIF select handling to reduce the overall complexity while maintaining functionality.