Need to bound execution time

[sparkprime]

It is currently possible to write programs that run for a long time, such as computing the Ackerman function. This is bad news if Jsonnet is integrated into a server, where such programs will use excess CPU resources and block other users.

Jsonnet should count the number of loops around the VM, and bound it either in number of instructions, or in time by calling the time syscall every 1000 instructions (or whatever).

[sparkprime]

The most reliable way to do this is, e.g. when evaluating Jsonnet server side, is to fork a new process to run Jsonnet (e.g. just run the standard commandline binary) and then ulimit that process.