How does this find an available port? Show me the actual implementation.

The main implementation is in [index.js:L89-L168], which exports the default getPort function. Here's how it works:

High-level flow:

1. Parse options [index.js:L90-L116]: Converts the port option to an array (if needed) and validates the exclude option to ensure it's an iterable of numbers.

2. Initialize port locking [index.js:L118-L129]: Sets up a timeout mechanism to release "young" locked ports after 15-30 seconds, moving them to "old" locked ports. This allows ports to be reused after a delay.

3. Iterate through candidates [index.js:L131-L161]: For each port in the sequence (preferred ports first, then random ones):

   • Skip excluded ports
   • Call getAvailablePort() to check if the port is actually available on all local hosts
   • If the port is locked, retry with a new random port (only if port is 0)
   • If successful and reserve is true, add to reservedPorts; otherwise add to lockedPorts.young
   • Return the available port

4. Handle failures [index.js:L162-L165]: Only catch EADDRINUSE (port in use) and EACCES (permission denied) errors; re-throw others.

Port checking logic [index.js:L61-L78] (getAvailablePort):

• If a specific host is given or port is 0, check that single host
• Otherwise, iterate through all local hosts and verify the port is available on all of them using checkAvailablePort()

Port locking mechanism: Ports are temporarily locked for 15-30 seconds to prevent race conditions. The reserve option makes the lock permanent for the process lifetime.

FOLLOW_UPS:

• What does checkAvailablePort function do exactly?
• How does the portCheckSequence function work?
• What are the "local hosts" checked by default?