util: Add a pprof helper package

As it turns out, there are other helper packages out there. I wrote this
before I realized that, and it didn't take me that long anyways.

main.go

@@ -43,7 +43,8 @@ import (
 	_ "github.com/purpleidea/mgmt/lang/gapi"         // import so the gapi registers
 	_ "github.com/purpleidea/mgmt/puppet"            // import so the gapi registers
 	_ "github.com/purpleidea/mgmt/puppet/langpuppet" // import so the gapi registers
-	_ "github.com/purpleidea/mgmt/yamlgraph"         // import so the gapi registers
+	"github.com/purpleidea/mgmt/util/pprof"
+	_ "github.com/purpleidea/mgmt/yamlgraph" // import so the gapi registers
 	"go.etcd.io/etcd/server/v3/etcdmain"
 )
 
@@ -76,6 +77,16 @@ func main() {
 		return              // for safety
 	}
 
+	// Run profiling if it's activated.
+	// TODO: Should we pass a logger into this?
+	ctx, cancel := context.WithCancel(context.Background())
+	if err := pprof.Run(ctx); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+		//return // redundant
+	}
+	defer cancel()
+
 	cliUtil.LogSetup(debug)
 	data := &cliUtil.Data{
 		Program: program,

util/pprof/pprof.go

@@ -0,0 +1,95 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+// Package pprof is a simple wrapper around the pprof utility code which we use.
+package pprof
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"runtime/pprof"
+	"strings"
+	"syscall"
+)
+
+// Run looks in a special environment var for the path to log pprof data to and
+// if it finds it, it begins profiling. If it doesn't find a special environment
+// var, it returns nil. If this is not able to start logging, then it errors. If
+// it starts logging, this waits for an exit signal in a goroutine and returns
+// nil. The magic env name is MGMT_PPROF_PATH. Example usage:
+// MGMT_PPROF_PATH="~/pprof/out.pprof" ./mgmt run lang examples/lang/hello.mcl
+// go tool pprof -no_browser -http :10000 ~/pprof/out.pprof
+func Run(ctx context.Context) error {
+	s := os.Getenv("MGMT_PPROF_PATH")
+	logf := func(format string, v ...interface{}) {
+		// TODO: is this a sane prefix to use here?
+		log.Printf(format, v...) // XXX: use parent logger when available
+	}
+
+	if s == "" || !strings.HasPrefix(s, "/") {
+		return nil // not activated
+	}
+	logf("pprof logging to: %s", s)
+
+	f, err := os.Create(s)
+	if err != nil {
+		return fmt.Errorf("could not create CPU profile: %v", err)
+	}
+	if err := pprof.StartCPUProfile(f); err != nil {
+		return fmt.Errorf("could not start CPU profile: %v", err)
+	}
+
+	signals := make(chan os.Signal, 1+1) // 1 * ^C + 1 * SIGTERM
+	signal.Notify(signals, os.Interrupt) // catch ^C
+	//signal.Notify(signals, os.Kill) // catch signals
+	signal.Notify(signals, syscall.SIGTERM)
+
+	go func() {
+		defer func() {
+			if err := f.Close(); err != nil {
+				logf("pprof write error: %v", err)
+				return
+			}
+			logf("pprof wrote file to: %s", s)
+		}()
+		defer pprof.StopCPUProfile()
+		select {
+		case sig := <-signals: // any signal will do
+			logf("pprof logging shutdown by sig: %v", sig)
+
+		case <-ctx.Done():
+			logf("pprof logging shutdown by ctx: %v", ctx.Err())
+		}
+	}()
+
+	return nil
+}