agent-signals

044. The agy presence file is a flock lock

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Date
2026-10-30
Agents
Antigravity CLI
Measured on
real machine

Measured

2026-10-30, Antigravity CLI (agy) 1.4.7, on Linux (Debian 13, x64), in a private tmux server with a throwaway HOME and a copied login. The scenarios scenarios/agy/deny-and-tools.sh (two runs) and scenarios/agy/continue.sh (one run, three processes) ran, at each step, flock -n <file> true on each file in ~/.gemini/antigravity-cli/presence/, from another process. They also listed the lines of /proc/locks for the inode of each file in presence/ and conversations/. Both only read. Measured on: real machine.

What was measured

  1. While agy ran, flock -n on presence/<conversation id>.lock exited with 1: another process held the lock. /proc/locks showed one FLOCK ADVISORY WRITE lock on the file. This was so at each step: busy, a dialog, after a turn, and after an Esc.
  2. After the process exited, flock -n exited with 0, and /proc/locks showed no lock. The file stayed, with size 0.
  3. A new session made the file and took the lock at the first prompt. Before the first prompt, presence/ had no file. A process started with --continue or --conversation <id> took the lock at the start (fact 43).
  4. conversations/<conversation id>.db and its -shm file each had one POSIX ADVISORY READ lock while agy ran. The -wal file had none.

Mechanism

agy takes an exclusive flock lock on the presence file and keeps it until the process exits. The kernel drops the lock when the process ends, also after a crash. A reader can test whether a conversation is open in a live process with flock -n <file> true: exit 1 means open. The test changes nothing, and it needs no process list. The file alone does not show this: it stays after the exit.

The POSIX read locks on the .db and -shm files are the locks of SQLite in WAL mode.

Incident

None recorded.

Screens

None.

Not measured