rustdoc spawns too many threads

[catamorphism]

If I don't configure with docs disabled, my machine becomes unresponsive when I do a make check and it gets to building the docs. Just now, I had to reboot because it was completely frozen for about 5-8 minutes.

MacBook Pro with OS 10.7, 4 GB of RAM. Sorry, don't have better information than this right now, but I wanted to report it.

[catamorphism]

I narrowed down the problem slightly: rustdoc spawns a ton of pandoc threads (over 20); each one uses 12 MB of memory and that causes my machine to thrash (apparently 4 GB of physical RAM isn't enough...)

Perhaps there should be some limit on the number of live threads rustdoc can spawn at once.

[eholk]

I ran into this problem this morning too.

[brson]

But they are in parallel! Isn't that awesome? I guess we'll have to add a worker task to the markdown pass to meter out pandoc processes.