Emscripten buildbot: PyRepl test failed with: http://localhost:8787 is already used

[vstinner]

On "WASM Emscripten 3.x" buildbot, the "PyRepl in Chrome smoke test" step failed with: https://buildbot.python.org/#/builders/1810/builds/2113

Error: http://localhost:8787 is already used, make sure that nothing is running on the port/url or set reuseExistingServer:true in config.webServer.

The buildbot configuration allows 4 builds in parallel:

        cpw(
            name="rkm-emscripten",
            tags=['emscripten'],
            not_branches=['3.10', '3.11', '3.12', '3.13'],
            parallel_builders=4,
        ),

So it's possible that 2 builds were running "PyRepl in Chrome smoke test" in parallel.

The port number 8787 is hardcoded in Platforms/emscripten/browser_test/playwright.config.ts:

$ grep 8787 Platforms/emscripten/browser_test/playwright.config.ts
    baseURL: 'http://localhost:8787',
    command: 'npx http-server ../../../cross-build/wasm32-emscripten/build/python/web_example_pyrepl_jspi/ -p 8787',
    url: 'http://localhost:8787',

cc @hoodmane @freakboy3742

[freakboy3742]

Agreed that seems a likely cause. I guess that means we need either:

1. a dynamically allocated (or at least configurable) port number
2. a lock around running that one test
3. Remove parallelism in the buildbot to

I'd rather avoid option (3); but I'm not sure how complex (1) or (2) would be - I'm not overly familiar with node tooling in that space.