Fix index.lock contention caused by git update-index on every FSEvents notification - #547

#!/bin/bash
# Reproduce GitX index.lock contention bug.
#
# Two modes:
#   --simulate   self-contained: runs update-index in a tight loop to mimic old GitX
#   (default)    tests real GitX: open the printed repo path in GitX commit view, press Enter
#
# Design:
#   - Large repo (500 files) so update-index --refresh takes longer -> wider lock window
#   - Background writer loop modifies files every 0.2s to keep FSEvents firing continuously
#   - Foreground loop hammers "git add" independently of the writer
#   - Also polls .git/index.lock directly (catches contention even if git add retries)

set -euo pipefail

SIMULATE=0
ITERATIONS=500
[[ "${1:-}" == "--simulate" ]] && SIMULATE=1

REPO=$(mktemp -d)
WRITER_PID=""
GITX_SIM_PID=""

cleanup() {
    [[ -n "$WRITER_PID" ]] && kill "$WRITER_PID" 2>/dev/null || true
    [[ -n "$GITX_SIM_PID" ]] && kill "$GITX_SIM_PID" 2>/dev/null || true
    rm -rf "$REPO"
}
trap cleanup EXIT

cd "$REPO"
git init -q
git config user.email "[email protected]"
git config user.name "Test"

echo "==> Creating 500-file repo (wider lock window for update-index)..."
for i in $(seq 1 500); do
    echo "file $i" > "file_$i.txt"
done
git add .
git commit -q -m "init"

echo "    Repo: $REPO"
echo ""

# Background writer: modifies files every 0.2s to keep FSEvents firing.
# Decoupled from the git add loop so FSEvents fires throughout the entire test.
start_writer() {
    while true; do
        for i in 1 50 100 200 300 400 500; do
            echo "$RANDOM" > "file_$i.txt"
        done
        sleep 0.2
    done
}

if [[ $SIMULATE -eq 1 ]]; then
    echo "==> Simulating OLD GitX behavior (update-index in tight loop)..."
    while true; do
        git update-index -q --unmerged --ignore-missing --refresh 2>/dev/null
    done &
    GITX_SIM_PID=$!
    start_writer &
    WRITER_PID=$!
else
    echo "==> Open this repo in GitX and switch to the Commit tab:"
    echo "    $REPO"
    echo ""
    echo "    Press Enter when ready..."
    read -r
    start_writer &
    WRITER_PID=$!
    echo "    File writer started (keeps FSEvents firing every 0.2s)"
fi

echo ""
echo "==> Running $ITERATIONS rapid 'git add' attempts..."
echo ""

LOCK_ERRORS=0
SUCCESS=0

for i in $(seq 1 $ITERATIONS); do
    echo "change $i" > "file_1.txt"
    ERR=$(git add file_1.txt 2>&1 || true)
    if echo "$ERR" | grep -q "index.lock"; then
        LOCK_ERRORS=$((LOCK_ERRORS + 1))
        if [[ $LOCK_ERRORS -le 3 ]]; then
            echo "  [attempt $i] LOCK ERROR"
        fi
    else
        SUCCESS=$((SUCCESS + 1))
    fi
done

echo ""
echo "Results: $SUCCESS succeeded, $LOCK_ERRORS lock errors / $ITERATIONS attempts"
echo ""

if [[ $LOCK_ERRORS -gt 0 ]]; then
    echo "FAIL: index.lock contention detected -- bug is present"
    exit 1
else
    echo "PASS: no lock contention detected"
    echo "      (run 3x to be confident -- race is timing-dependent)"
    exit 0
fi