Enable blocking profiles. (#3957)

Per https://golang.org/pkg/runtime/#SetBlockProfileRate, to use blocking
profiling we need to set a profile rate. This enables it at once per
second. This might help us debug the problem where Publisher sometimes
stalls on submitting to all logs.

cmd/boulder-publisher/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"os"
+	"runtime"
 	"time"
 
 	ct "github.com/google/certificate-transparency-go"
@@ -19,6 +20,10 @@ type config struct {
 	Publisher struct {
 		cmd.ServiceConfig
 		Features map[string]bool
+		// If this is non-zero, profile blocking events such that one even is
+		// sampled every N nanoseconds.
+		// https://golang.org/pkg/runtime/#SetBlockProfileRate
+		BlockProfileRate int
 	}
 
 	Syslog cmd.SyslogConfig
@@ -46,6 +51,8 @@ func main() {
 	err = features.Set(c.Publisher.Features)
 	cmd.FailOnError(err, "Failed to set feature flags")
 
+	runtime.SetBlockProfileRate(c.Publisher.BlockProfileRate)
+
 	if *grpcAddr != "" {
 		c.Publisher.GRPC.Address = *grpcAddr
 	}

test/config-next/publisher.json

@@ -1,5 +1,6 @@
 {
   "publisher": {
+    "blockProfileRate": 1000000000,
     "maxConcurrentRPCServerRequests": 100000,
     "submissionTimeout": "5s",
     "debugAddr": ":8009",