Two `nvm install <same version>` runs could race on the version directory
- one removing or replacing it while the other reads or writes it.
Take a per-version advisory lock
(an atomically-created directory under $NVM_DIR/.cache locks)
around the binary/source install,
so a second run of the same version waits for the first;
installs of different versions never contend.
NVM_INSTALL_LOCK_TIMEOUT (seconds, default 600) bounds the wait,
after which nvm reports the lock path so a lock left by a killed install can be removed.
NVM_INSTALL_LOCK_STALE (minutes, default 0 / off)
opts into automatically stealing a lock older than that,
for unattended or CI use.
Jordan Harband
809f3ee5ab