NEW FEATURE: Gather data for providers concurrently

[tlimoncelli]

Goal: collect "preview" information in parallel to improve dnscontrol peformance.

• dnscontrol ppreview -- Like preview, but collects data in parallel for providers that permit it.
• dnscontrol ppush -- Like ppreview but pushes
• Flags:
  • --cmode=none Don't do any work concurrently (useful when you find a bug)
  • --cmode=all Run all providers concurrently (dangerous!)

NOTE: Eventually ppreview and ppush will replace preview and push. These are temporary commands. We'll probably do 1-2 public releases with the pp versions before we remove the non-parallel verions.

How to test this

Here's how to try the changes:

$ git clone https://github.com/StackExchange/dnscontrol.git$ cd dnscontrol
$ git checkout tlim_parallel$ go install
$ (cd to where your dnsconfig.js is)
$ dnscontrol preview                 # Old code$ dnscontrol ppreview --cmode=none   # New code, one provider at a time
$ dnscontrol ppreview                # New code, gather data concurrently when safe
$ dnscontrol ppreview --cmode=all    # New code, gather data concurrently no matter what! (unsafe!)

Is your provider safe to run concurrently?

Look for this line in the source file:

providers.CanConcur:              providers.Cannot(),

If you see providers.Can() then your provider has already been tested and verified to be working.

If you'd like to test your provider, change Cannot() to Can() and compile with the -race flag. This will attempt to detect any race conditions.

cd /my/source/code
vim provider/foo/fooProvider.go       # Change Cannot to Can
go install -race

cd /my/dns/config
dnscontrol ppreview --full

Please report any bugs, suggestions, or performance results in the comments below.

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