fix: do not subscribe to process signal handlers unless necessary

Fixes moxystudio#111

lib/lockfile.js

@@ -248,6 +248,8 @@ function lock(file, options, callback) {
                     lastUpdate: Date.now(),
                 };
 
+                ensureTeardown();
+
                 // We must keep the lock fresh to avoid staleness
                 updateLock(file, options);
 
@@ -326,15 +328,24 @@ function getLocks() {
     return locks;
 }
 
-// Remove acquired locks on exit
-/* istanbul ignore next */
-onExit(() => {
-    for (const file in locks) {
-        const options = locks[file].options;
+let hasTeardown = false;
 
-        try { options.fs.rmdirSync(getLockFile(file, options)); } catch (e) { /* Empty */ }
-    }
-});
+function ensureTeardown() {
+    if (hasTeardown) { return; }
+    hasTeardown = true;
+
+    // Remove acquired locks on exit.
+    // Do not setup exit listeners unless there's a need since they subscribe to
+    // node.js signal handlers and change default node.js behavior when handling signals.
+    /* istanbul ignore next */
+    onExit(() => {
+        for (const file in locks) {
+            const options = locks[file].options;
+
+            try { options.fs.rmdirSync(getLockFile(file, options)); } catch (e) { /* Empty */ }
+        }
+    });
+}
 
 module.exports.lock = lock;
 module.exports.unlock = unlock;