René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"MCP server processes orphaned when parent (Claude CLI) dies — 4GB memory leak","articleBody":"## Problem\n\nWhen XcodeBuildMCP is launched as an MCP server via `npm exec xcodebuildmcp@latest mcp` (as Claude Code does), the process persists indefinitely after the parent process exits. Each orphaned instance consumes up to **4GB of resident memory**.\n\nThis is especially painful when running multiple Claude Code sessions — orphaned `xcodebuildmcp` processes accumulate and grind the system to a halt.\n\n```\n$ ps aux | grep xcodebuild\ndale  24113 352.3 23.5 450778096 3945760  ??  R  3:59PM  1:15.03 node ...xcodebuildmcp mcp\ndale  24114   0.0  0.3 446631664  48928   ??  S  3:59PM  0:00.84 node ...xcodebuildmcp mcp\ndale  24053   0.0  0.3 435888672  47712   ??  S  3:59PM  0:00.63 npm exec xcodebuildmcp@latest mcp\ndale  24052   0.0  0.3 435888944  47712   ??  S  3:59PM  0:00.64 npm exec xcodebuildmcp@latest mcp\n```\n\n## Root Cause\n\n`start-mcp-server.js` relies on `stdin` end/close events to detect parent death (lines 99–104). However, when spawned through `npm exec`, there's an intermediate node wrapper process. When the parent (Claude CLI) dies:\n\n1. The `npm exec` wrapper becomes orphaned (reparented to launchd/PID 1)\n2. The wrapper doesn't close its stdin pipe to the actual xcodebuildmcp process\n3. The MCP server never receives the stdin end/close event\n4. The process runs forever with no work to do\n\nAdditionally, unlike daemon mode (which has `idle-shutdown.js` with a 10-minute timeout), the MCP server mode has **no idle timeout at all**.\n\n## Suggested Fix\n\nAdd a parent-PID watchdog to `start-mcp-server.js`. When the parent process dies, macOS/Linux reparents the child to init/launchd (PID 1). Polling `process.ppid` detects this:\n\n```diff\n--- a/src/server/start-mcp-server.ts\n+++ b/src/server/start-mcp-server.ts\n@@ in startMcpServer(), after enrichSentryContext() and before shuttingDown declaration\n+    // Parent-process watchdog: detect orphaned process when parent dies.\n+    // When the parent (Claude CLI / npm exec) exits, the OS reparents us to\n+    // init/launchd (PID 1). Poll every 5s and shut down if that happens.\n+    const originalPpid = process.ppid;\n+    const ppidWatchdog = setInterval(() =\u003e {\n+      if (process.ppid !== originalPpid) {\n+        clearInterval(ppidWatchdog);\n+        log(\"info\", `Parent process died (was ${originalPpid}, now ${process.ppid}); shutting down`);\n+        void shutdown(\"parent-died\");\n+      }\n+    }, 5000);\n+    ppidWatchdog.unref(); // Don't keep the event loop alive just for this\n```\n\nThis is 8 lines, zero dependencies, works on macOS and Linux, and has no effect during normal operation.\n\n## Environment\n\n- macOS 15 (Darwin 25.3.0), Apple Silicon\n- XcodeBuildMCP 2.2.1\n- Claude Code 2.1.75 (VS Code extension)\n- Launched via: `npm exec xcodebuildmcp@latest mcp`\n\n🤖 Generated with [Claude Code](https://claude.com/claude-code)","author":{"url":"https://github.com/dalegass","@type":"Person","name":"dalegass"},"datePublished":"2026-03-14T01:30:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/273/XcodeBuildMCP/issues/273"}