Fix #700: Remove public Clone from spsc_queue to prevent memory corruption

[dahankzter]

Summary

Fixes #700 - Removes the public Clone implementation from Producer<T> and Consumer<T> to prevent memory corruption in safe code.

Problem

The spsc_queue is designed for Single-Producer-Single-Consumer access with Ordering::Relaxed for performance. The public Clone trait implementation allowed external code to create multiple producers or consumers, which violates SPSC guarantees and causes:

• Double-free when multiple consumers read the same value from the queue
• Heap corruption (malloc(): chunk size mismatch in fastbin)
• Memory leaks when multiple producers overwrite values without dropping
• Undefined behavior in safe Rust code

Solution

1. Removed Clone trait implementation from Producer<T> and Consumer<T>
2. Added crate-private clone_internal() methods for internal use within glommio
3. Updated shared_channel to use clone_internal() for connection handoff
4. Added documentation explaining SPSC guarantees and safety requirements

Breaking Change

This is a breaking API change. External code that clones Producer or Consumer will no longer compile. However, such code was already unsound and could cause heap corruption.

Internal uses within glommio (e.g., shared_channel) are safe because they ensure only one producer/consumer is active at any given time.

Testing

• All existing tests pass
• The reproduction case from Memory corruption in glommio::channels::spsc_queue under concurrent use #700 now correctly fails to compile (preventing the bug)
• Verified in Linux container with kernel 6.16 and io_uring support

[dahankzter]

All failures show the same error:
Os { code: 95, kind: Unsupported, message: "Operation not supported" }
Operation: "Reading" from DMA files

This occurs because:

• DMA files require O_DIRECT support (direct I/O)
• GitHub Actions CI runs tests on /tmp (likely tmpfs/overlayfs)
• These filesystems don't support O_DIRECT operations
• The test output even warns: "Glommio currently only supports NVMe-backed volumes formatted with XFS or EXT4"

[henrik-leovegas]

Update: Rebased on PR #702

This PR has been rebased on top of #702 (dependency updates) to inherit its passing CI infrastructure.

What changed from the rebase:

From PR #702 (most of the file changes):

• Updated dependencies including rand from 0.10 to 0.9
• Various other dependency and infrastructure updates
• This explains why the PR shows 617 additions / 537 deletions across 43 files

Our actual fix (the core changes for issue #700):

• glommio/src/channels/spsc_queue.rs - Removed public Clone, added clone_internal()
• glommio/src/channels/shared_channel.rs - Updated to use clone_internal()
• glommio/benches/shared_channel.rs & glommio/benches/competing_io.rs - Fixed for rand 0.9 API

All CI checks now pass ✅