Add support for synchronous and asynchronous modes in package cache

- Introduced a new command-line argument `--pkg-cache-mode` to specify caching mode.
- Allows users to choose between 'sync' and 'async' modes, overriding the default configuration.
- Updated `add_variant` function to handle the new caching mode option.
- Ensures backward compatibility by maintaining default behavior when no mode is specified.

src/rez/cli/pkg-cache.py

@@ -41,6 +41,14 @@ def setup_parser(parser, completions=False):
  group.add_argument(
  "--daemon", action="store_true", help=SUPPRESS
  )
+ parser.add_argument(
+ "--pkg-cache-mode",
+ choices=["sync", "async"],
+ default=None,
+ help="If provided, override the rezconfig's package_cache_async key. "
+ "If 'sync', the process will block until packages are cached. "
+ "If 'async', the process will not block while packages are cached."
+ )
  parser.add_argument(
  "-c", "--columns", nargs='+', choices=column_choices,
  default=["status", "package", "variant_uri", "cache_path"],
@@ -70,7 +78,15 @@ def add_variant(pkgcache, uri, opts):
  print("No such variant: %s" % uri, file=sys.stderr)
  sys.exit(1)
 
- destpath, status = pkgcache.add_variant(variant, force=opts.force)
+ if opts.pkg_cache_mode is not None:
+ cache_mode = True if opts.pkg_cache_mode == "sync" else False
+ destpath, status = pkgcache.add_variant(
+ variant, force=opts.force,
+ wait_for_copying=cache_mode
+ )
+ # If no mode is specified, use the default behavior.
+ else:
+ destpath, status = pkgcache.add_variant(variant, force=opts.force)
 
  if status == PackageCache.VARIANT_FOUND:
  print_info("Already exists: %s", destpath)