Close the pty controller fd on dispose

[JohnCampionJr]

Every pseudoterminal leaks its controller file descriptor for the life of the process.

PtyStream wraps the fd with ownsHandle: false, which is correct — ReaderStream and WriterStream are two streams over the same fd, and letting either own it would make disposing both a double close.

The consequence is that disposing them closes neither, and nothing else closes it either: pty_close exists in the native shim and is declared in both Mac and Linux NativeMethods, and has no callers anywhere in the library.

How it shows up

As pty_spawn failing after enough terminals have come and gone — which reads as a system limit rather than as a leak, and reads that way most convincingly in exactly the long-lived process that leaks the most.

Found by moving a test suite into a single process, where several tests each opening a batch of ptys ran back to back. Each test alone had always been fine.

On the ordering

Streams, then kill, then close. The streams don't own the fd; the kill wants the process still addressable; closing the controller last means nothing reads from a descriptor that has gone. TryClose never throws, matching TryKill beside it — a cleanup path isn't a place to discover a new failure.

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Companion to #7 (forkpty thread safety) but independent of it — either can go in alone.

[Copilot]

🟡 Changes recommended

Synchronize disposal or atomically invalidate the descriptor before closing to prevent unsafe double closes.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR closes leaked Unix PTY controller file descriptors during disposal on macOS and Linux.

Changes:

• Adds disposal-time controller descriptor cleanup.
• Preserves cleanup ordering: streams, process termination, then descriptor closure.
• Implements platform-specific close operations.

File summaries

File	Summary
src/Porta.Pty/Unix/PtyConnection.cs	Adds controller descriptor cleanup; disposal is not synchronized, risking a double close and incorrect closure of a reused descriptor.
src/Porta.Pty/Mac/PtyConnection.cs	Implements macOS descriptor closing.
src/Porta.Pty/Linux/PtyConnection.cs	Implements Linux descriptor closing.

Review details

Suppressed comments (2)

src/Porta.Pty/Unix/PtyConnection.cs:95

• This resource-lifetime fix has no regression test: the existing tests dispose connections incidentally via using, but none repeatedly spawn and dispose PTYs in one process or assert that the controller descriptor is reclaimed. Add a Unix-focused stress/regression test that exercises repeated disposal and detects descriptor exhaustion or an unbounded descriptor count, so this leak cannot be reintroduced unnoticed.

            this.TryClose();

src/Porta.Pty/Unix/PtyConnection.cs:95

• If either FileStream.Dispose() throws while flushing the writer (for example after the child has already closed the slave), control exits Dispose before reaching this line. Because isDisposed was already set, a later Dispose returns immediately, leaving the controller fd leaked. Put the stream disposal in a try/finally whose cleanup always runs TryKill and TryClose (and ensure both streams are attempted).

            this.TryClose();

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[tomlm]

This maybe should be fixed