Launch emulator in signal-isolated process on Unix to survive Ctrl+C

[Copilot]

Ctrl+C of dotnet run kills the Android emulator because the terminal sends SIGINT to the entire process group, including the child emulator process.

Changes

• Signal isolation on Unix: Wrap emulator launch through /bin/sh -c 'trap "" INT; exec ...'. trap '' INT sets SIGINT to SIG_IGN, which POSIX guarantees is preserved across exec. The emulator process ignores SIGINT from the parent terminal while remaining killable via adb emu kill or window close. exec replaces the shell so the Process object tracks the correct PID.

• Windows unchanged: Ctrl+C propagation works differently on Windows; no wrapper needed.

• Bug fix: BootEmulatorAsync accessed emulatorProcess.ExitCode after Dispose() — save exit code before disposing.

• Shell quoting: Added ShellQuote() for proper POSIX single-quote escaping of emulator path and arguments.

// Before: emulator inherits parent's process group and receives SIGINT
psi = ProcessUtils.CreateProcessStartInfo(emulatorPath, args.ToArray());

// After (Unix): emulator ignores SIGINT via SIG_IGN preserved across exec
var shellCmd = new StringBuilder("trap '' INT; exec ");
shellCmd.Append(ShellQuote(emulatorPath));
foreach (var arg in args) {
    shellCmd.Append(' ');
    shellCmd.Append(ShellQuote(arg));
}
psi = ProcessUtils.CreateProcessStartInfo("/bin/sh", "-c", shellCmd.ToString());

Tests

• LaunchEmulator_SurvivesSigint — sends SIGINT to the launched process, asserts it remains alive
• ShellQuote_EscapesSingleQuotes — verifies paths containing ' work correctly

[jonathanpeppers]

I investigated P/Invoke alternatives and none work cleanly:

Approach	Problem
setpgid(childPid, childPid) from parent after Process.Start()	Race condition — child may have already exec'd, causing EACCES
signal(SIGINT, SIG_IGN) before Start(), restore after	Conflicts with .NET runtime signal handling; parent briefly ignores SIGINT
ProcessStartInfo.CreateNewProcessGroup	Throws PlatformNotSupportedException on Unix (all .NET versions including 11)
/usr/bin/setsid <emulator>	Not available on macOS
Manual fork()/exec() via P/Invoke	Extremely complex, fragile in managed code

The core issue is that .NET's Process class has no pre-exec hook (unlike Python's preexec_fn), so there's no way to call setsid() or signal(SIGINT, SIG_IGN) in the child between fork and exec.

The trap '' INT; exec pattern used here is the well-established POSIX idiom for this:

1. trap '' INT sets SIGINT to SIG_IGN in the shell
2. exec replaces the shell with the emulator
3. POSIX guarantees SIG_IGN is preserved across exec (POSIX.1-2017 Section 2.4.3):

   "Any signals that had been set to be ignored (SIG_IGN) shall remain ignored."

See also: POSIX trap utility, Austin Group Bug #152

[jonathanpeppers]

/review

[github-actions]

✅ Android Tools PR Reviewer completed successfully!

[Copilot]

Pull request overview

This PR updates Xamarin.Android.Tools.AndroidSdk’s emulator launching behavior on Unix so the Android emulator won’t be terminated by Ctrl+C sent to the parent terminal’s process group, while keeping Windows behavior unchanged. It also tightens emulator boot failure reporting and adds targeted Unix-only tests to validate the SIGINT-survival and shell-quoting behavior.

Changes:

• On Unix, launch the emulator via /bin/sh -c "trap '' INT; exec ..." and add POSIX-safe single-quote escaping via ShellQuote().
• Fix BootEmulatorAsync to avoid reading Process.ExitCode after disposing the process handle.
• Update/extend tests to validate SIGINT survival on Unix and correct handling of emulator paths containing single quotes.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Xamarin.Android.Tools.AndroidSdk/Runners/EmulatorRunner.cs	Wrap Unix emulator launch in a SIGINT-ignoring shell+exec command; fix exit-code capture before dispose; add POSIX shell quoting helper.
tests/Xamarin.Android.Tools.AndroidSdk-Tests/EmulatorRunnerTests.cs	Adjust launch-failure assertion to check ErrorKind; add Unix-only tests for SIGINT survival and quoting of paths containing '.

[github-actions]

🤖 ✅ LGTM — Clean, well-reasoned change.

Summary: The SIGINT isolation via trap '' INT; exec is the correct POSIX approach, and the ShellQuote implementation uses the canonical single-quote escaping pattern. The ExitCode-after-Dispose() bug fix is a genuine catch. The test for SIGINT survival is well-designed — it verifies the core behavior by sending a real signal and checking the process remains alive.

Suggestions (non-blocking):

• 💡 Move the two new tests above the // --- Helpers --- separator to keep test/helper sections distinct
• ⚠️ Add process kill logic to the finally blocks in both new tests to match the cleanup pattern used by existing tests and avoid potential process leaks in CI

Severity	Count
❌ Error	0
⚠️ Warning	1 (test cleanup)
💡 Suggestion	2

Positive callouts:

• The exec trick preserves the Process PID tracking while achieving signal isolation — avoids the complexity of P/Invoke or process group management
• Saving ExitCode before Dispose() prevents a real ObjectDisposedException
• Good test coverage: both the SIGINT survival and the single-quote-in-path edge case

Generated by Android Tools PR Reviewer for issue #361 · ● 2.3M

[jonathanpeppers]

Test passes on macOS:

[jonathanpeppers]

I think this will fix this problem, but I'm open to other solutions than this trap command.

I couldn't get copilot to find an alternative:

• #361 (comment)