Add parallel copy option to build-and-copy.sh

Introduced the --copy-parallel flag to enable concurrent copying of Docker images to multiple hosts. Updated the README with usage instructions and details about the new option. Refactored the script to support both serial and parallel copy modes for improved efficiency.

README.md

@@ -14,8 +14,9 @@ The Dockerfile builds from the main branch of VLLM, so depending on when you run
 
 ### 2025-12-18
 
-Updated `build-and-copy.sh` to support copying to multiple hosts. 
+Updated `build-and-copy.sh` to support copying to multiple hosts.
 - Added `-c, --copy-to` (accepts space- or comma-separated host lists) and kept `--copy-to-host` as a backward-compatible alias.
+- Added `--copy-parallel` to copy to all hosts concurrently.
 - Short `-h` is now used for help.
 
 ### 2025-12-15
@@ -99,6 +100,12 @@ Copy to multiple hosts (space- or comma-separated after the flag):
 ./build-and-copy.sh --copy-to 192.168.177.12 192.168.177.13
 ```
 
+Copy to multiple hosts in parallel:
+
+```bash
+./build-and-copy.sh --copy-to 192.168.177.12 192.168.177.13 --copy-parallel
+```
+
 Using a different username:
 
 ```bash
@@ -146,6 +153,7 @@ Using a different username:
 | `--vllm-ref <ref>` | vLLM commit SHA, branch or tag (default: 'main') |
 | `-c, --copy-to <host[,host...] or host host...>` | Host(s) to copy the image to after building (space- or comma-separated list after the flag). |
 | `--copy-to-host` | Alias for `--copy-to` (backwards compatibility). |
+| `--copy-parallel` | Copy to all specified hosts concurrently. |
 | `-u, --user <user>` | Username for SSH connection (default: current user) |
 | `--no-build` | Skip building, only copy existing image (requires `--copy-to`) |
 | `-h, --help` | Show help message |