bxcore, loopd, inferproxy: a lock file keeps each to one instance

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/inferproxy/src/main.rs

@@ -4,6 +4,7 @@ use std::os::unix::fs::PermissionsExt;
 use std::path::PathBuf;
 use std::process;
 
+use bxcore::instance;
 use inferproxy::{Limits, serve};
 
 fn main() {
@@ -39,6 +40,19 @@ fn main() {
     };
 
     let path: PathBuf = listen.into();
+    // One inferproxy per socket (M5b spec, section 9a): the lock beside the socket comes before
+    // the stale socket is removed, so a second copy never takes the socket of the one that runs.
+    // Held until the process ends; `process::exit` leaves it to the system to release.
+    let mut lock_path = path.clone().into_os_string();
+    lock_path.push(".lock");
+    let lock_path = PathBuf::from(lock_path);
+    let _instance = match instance::lock(&lock_path) {
+        Ok(held) => held,
+        Err(e) => {
+            eprintln!("{}", e.line("inferproxy", &lock_path));
+            process::exit(1);
+        }
+    };
     match fs::remove_file(&path) {
         Ok(()) => {}
         Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}