From c3b9b31f9d0b1cc27ada118b7c48986a32707368 Mon Sep 17 00:00:00 2001
From: Mark Rappoport <markr@inspekto.com>
Date: Mon, 9 Aug 2021 17:12:02 +0300
Subject: [PATCH 1/2] allow adjustable number of rendering workers via
 MAX_WORKERS envar

---
 report/report.go | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/report/report.go b/report/report.go
index 9d354a5..eb2d88f 100644
--- a/report/report.go
+++ b/report/report.go
@@ -20,9 +20,12 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"math"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
+	"strconv"
 	"sync"
 	"text/template"
 
@@ -72,6 +75,15 @@ func new(g grafana.Client, dashName string, time grafana.TimeRange, texTemplate
 	return &report{g, time, texTemplate, dashName, tmpDir, ""}
 }
 
+func (rep *report) getWorkerNum() int {
+	var (
+		desiredWorkers, _ = strconv.Atoi(os.Getenv("MAX_WORKERS"))
+		maxWorkers = runtime.NumCPU()
+	)
+	desiredWorkers = int(math.Max(1, math.Min(float64(desiredWorkers), float64(maxWorkers))))
+	return desiredWorkers
+}
+
 // Generate returns the report.pdf file.  After reading this file it should be Closed()
 // After closing the file, call report.Clean() to delete the file as well the temporary build files
 func (rep *report) Generate() (pdf io.ReadCloser, err error) {
@@ -141,8 +153,7 @@ func (rep *report) renderPNGsParallel(dash grafana.Dashboard) error {
 	//limit concurrency using a worker pool to avoid overwhelming grafana
 	//for dashboards with many panels.
 	var wg sync.WaitGroup
-	workers := 5
-	wg.Add(workers)
+	wg.Add(rep.getWorkerNum())
 	errs := make(chan error, len(dash.Panels)) //routines can return errors on a channel
 	for i := 0; i < workers; i++ {
 		go func(panels <-chan grafana.Panel, errs chan<- error) {

From b70b07b53416c74185c76cfad6a5b3c5dbeb97e4 Mon Sep 17 00:00:00 2001
From: Mark R <github@mark.org.il>
Date: Mon, 9 Aug 2021 20:15:22 +0300
Subject: [PATCH 2/2] Cleanup worker assignment

---
 report/report.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/report/report.go b/report/report.go
index eb2d88f..d7e55b0 100644
--- a/report/report.go
+++ b/report/report.go
@@ -142,6 +142,10 @@ func (rep *report) texPath() string {
 }
 
 func (rep *report) renderPNGsParallel(dash grafana.Dashboard) error {
+	var (
+		wg sync.WaitGroup
+		workers = rep.getWorkerNum()
+	)
 	//buffer all panels on a channel
 	panels := make(chan grafana.Panel, len(dash.Panels))
 	for _, p := range dash.Panels {
@@ -152,8 +156,8 @@ func (rep *report) renderPNGsParallel(dash grafana.Dashboard) error {
 	//fetch images in parrallel form Grafana sever.
 	//limit concurrency using a worker pool to avoid overwhelming grafana
 	//for dashboards with many panels.
-	var wg sync.WaitGroup
-	wg.Add(rep.getWorkerNum())
+	
+	wg.Add(workers)
 	errs := make(chan error, len(dash.Panels)) //routines can return errors on a channel
 	for i := 0; i < workers; i++ {
 		go func(panels <-chan grafana.Panel, errs chan<- error) {