At Microsoft, I watched (from afar) the incredibly painful multi-year process of making a complex language runtime intended for one environment (.NET for IIS) satisfy the requirements of a very different environment (SQL Server). When fundamental design assumptions like "memory allocation failures can kill the process" have to change, it's a big deal.
Seems like process isolation a la fastcgi is the practical way to go, unless the V8 team itself wants V8 to be embeddable in a "reliable" way (meaning, it recovers from its own errors without corrupting the process it's embedded in).
Seems like process isolation a la fastcgi is the practical way to go, unless the V8 team itself wants V8 to be embeddable in a "reliable" way (meaning, it recovers from its own errors without corrupting the process it's embedded in).