Description

Implements the approved API surface for SafeProcessHandle (#123380): process lifecycle management via Start, Open, Kill, Signal, SignalProcessGroup, and WaitForExit overloads. Windows implementation complete; Unix stubs throw NotImplementedException (separate PR).

ProcessStartOptions options = new("cmd.exe") { Arguments = { "/c", "echo hello" } };
using SafeProcessHandle handle = SafeProcessHandle.Start(options, input: null, output: null, error: null);
ProcessExitStatus status = handle.WaitForExit();
// status.ExitCode == 0, status.Canceled == false

Public API

• Open(int processId) — opens existing process handle
• Start(ProcessStartOptions, SafeFileHandle?, SafeFileHandle?, SafeFileHandle?) — create process with explicit stdio handles
• Kill() — terminate process
• Signal(PosixSignal) / SignalProcessGroup(PosixSignal) — send signal; accepts raw signal numbers like PosixSignalRegistration.Create
• WaitForExit(), TryWaitForExit(TimeSpan, out ProcessExitStatus?), WaitForExitOrKillOnTimeout(TimeSpan) — synchronous wait
• WaitForExitAsync(CancellationToken), WaitForExitOrKillOnCancellationAsync(CancellationToken) — async wait

Internal for now (pending follow-up): ProcessId, StartSuspended, Resume, KillProcessGroup.

Windows implementation

• STARTUPINFOEX + PROC_THREAD_ATTRIBUTE_HANDLE_LIST for explicit handle inheritance
• Job objects for KillOnParentExit and process group termination (best-effort emulation of Unix process groups)
• DangerousAddRef/DangerousRelease on InheritedHandles in PrepareHandleAllowList and on this in KillCore to prevent use-after-free races with concurrent Dispose
• Interlocked.Exchange for _threadHandle and _processGroupJobHandle in ReleaseHandle; Volatile.Read for _processGroupJobHandle access elsewhere
• Sync wait methods use WaitForSingleObject(SafeProcessHandle, ...) directly — no handle duplication via ProcessWaitHandle
• Async wait methods retain ProcessWaitHandle for RegisterWaitForSingleObject
• NativeMemory.Alloc with two-arg overflow-safe version; typed pointers (IntPtr*, void*)
• OOM-safe handle cleanup in finally; error check immediately after CreateProcess

Architecture — ProcessUtils as shared dependency

• ProcessUtils.cs holds s_processStartLock (ReaderWriterLockSlim) — avoids Process ↔ SafeProcessHandle dependency cycle
• ProcessUtils.Windows.cs holds BuildArgs(string, IList<string>?) and GetEnvironmentVariablesBlock
• Process.Windows.cs acquires write lock; SafeProcessHandle.Windows.cs acquires read lock

Interop additions

• Interop.JobObjects.cs, Interop.ProcThreadAttributeList.cs, Interop.ConsoleCtrl.cs (consolidated), Interop.HandleInformation.cs (extended), Interop.ResumeThread_IntPtr.cs, Interop.WaitForSingleObject_SafeProcessHandle.cs

Tests

• SafeProcessHandleTests.cs — start/kill/wait/timeout/signal tests with Nano Server support (ping fallback); signal tests as [Theory] with [InlineData]

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