Disable git fsmonitor in git_worker to fix hangs when fetching repositories

[luispadron]

This commit adds the -c core.fsmonitor=false arguments to all git commands (excluding git init) in git_worker.bzl. The purpose of this is to disable git from spawning a file system monitor, when many of these are spawned on a machine that is already under load or out of file descriptors, the git commands will hang indefinitely.

Fixes #21438

[luispadron]

I performed tests by spawning many file watchers using the fswatch tool, using a released Bazel version 7.3.1 when running bazel fetch in the examples/lots_of_repos directory of the branch: https://github.com/cgrindel/rules_swift_package_manager/tree/luis/lots-of-repo-example I was able to consistently reproduce stuck fetches.

I confirmed that building //src:bazel and using that instead consistently allows all fetches to continue and I ran into no hangs during the process.

---

#!/bin/bash

# Number of monitors to create
NUM_MONITORS=100  # Adjust based on your stress test needs

# Directory to monitor (can be the same or different for each monitor)
MONITOR_DIR="/tmp/fsmonitor-test"

# Create the directory if it doesn't exist
mkdir -p "$MONITOR_DIR"

# Array to store process IDs of background fswatch processes
declare -a PIDS

# Function to create and run a file system monitor
create_monitor() {
  local dir=$1
  fswatch "$dir" >/dev/null &
  PIDS+=($!)  # Store the process ID
}

# Create the specified number of monitors
for i in $(seq 1 $NUM_MONITORS); do
  create_monitor "$MONITOR_DIR"
  
  # Optionally, introduce a slight delay to avoid overwhelming the system too quickly
  sleep 0.1
done

echo "Created $NUM_MONITORS file system monitors."


# Function to clean up by killing all background processes
cleanup() {
  echo "Cleaning up monitors..."
  for pid in "${PIDS[@]}"; do
    kill "$pid" 2>/dev/null
  done
  echo "All monitors terminated."
}

# Trap script exit (Ctrl+C or normal exit) to ensure cleanup happens
trap cleanup EXIT

# Keep the script running to simulate long-running monitors
echo "Press Ctrl+C to stop the script and clean up the monitors."
while true; do
  sleep 10  # Keep the script alive indefinitely
done

[luispadron]

I moved the passing of git to be implied in this function as its intended to run git commands anyway. This allows me to add -c which must come directly after git without searching through the args we are given

[fmeum]

@bazel-io fork 7.4.0

[Wyverald]

nice! thanks for providing lots of context too, that really helps.