Stop checking for the existence of sha256sum

It should be in all coreutils packages...

gocrypt.bash

@@ -36,16 +36,27 @@ gocrypt_unique_task_identifier() {
     echo "pass-gocrypt-$(sha256sum <<< "$PREFIX" | cut -d ' ' -f 1)"
 }
 
+# This file is used as a lock for all access to the encrypted password store
+# so that it prevents the auto-close task from unmounting before all operations
+# are completed
+gocrypt_lock_file_path() {
+    local path="$XDG_RUNTIME_DIR"
+    if [ -z "$path" ] || [ ! -d "$path" ]; then
+        path="/tmp"
+    fi
+    echo "$path/$(gocrypt_unique_task_identifier).lck"
+}
+
 gocrypt_spawn_close_task() {
     which systemd-run > /dev/null || return
-    which sha256sum > /dev/null || return
 
     local task_name="$(gocrypt_unique_task_identifier)"
     # Cancel any previous task that might be present
     systemctl --user stop "$task_name.timer" > /dev/null 2>1
 
     # Create a new task
-    systemd-run --user --on-active=$gocrypt_close_timeout --unit="$task_name" /usr/bin/env bash -c \
+    systemd-run --user --on-active=$gocrypt_close_timeout --unit="$task_name" \
+        /usr/bin/env flock -x "$(gocrypt_lock_file_path)" /usr/bin/env bash -c \
         "fusermount -u '$PREFIX'/'$gocrypt_dec_dir' || fusermount -u -z '$PREFIX'/'$gocrypt_dec_dir'"
 
     echo "Will close the gocryptfs mount after $gocrypt_close_timeout seconds"
@@ -151,6 +162,7 @@ gocrypt_close() {
 }
 
 gocrypt_delegate() {
+    # Note: the caller MUST hold the lock for accessing the encrypted password store before calling
     gocrypt_open_check
     # Delegate command to another `pass` instance that manages what is inside of the mountpoint
     PASSWORD_STORE_DIR="$PWD/$gocrypt_dec_dir" "$PROGRAM" "$@"
@@ -236,6 +248,13 @@ fi
 # cd into the password store prefix
 cd "$PREFIX"
 
+# Open the lock file
+touch "$(gocrypt_lock_file_path)" || exit 1
+exec {lock_fd}< "$(gocrypt_lock_file_path)" || exit 1
+
+# Always take the exclusive lock while any command is running -- to prevent the close task from running at the same time
+flock -x $lock_fd
+
 case "$1" in
     help)
         gocrypt_help
@@ -264,3 +283,6 @@ case "$1" in
     *)
         gocrypt_die "Unknown command $1 for gocrypt"
 esac
+
+# Manual unlock; not strictly necessary since exit will also release the lock
+flock -u $lock_fd