Add fgprof pprof profiler (#20005)

fgprof is a sampling Go profiler that allows you to analyze On-CPU as
well as Off-CPU (e.g. I/O) time together.

Go's builtin sampling CPU profiler can only show On-CPU time, but it's
better than fgprof at that. Go also includes tracing profilers that can
analyze I/O, but they can't be combined with the CPU profiler.

fgprof is designed for analyzing applications with mixed I/O and CPU
workloads. This kind of profiling is also known as wall-clock profiling.

Whilst fgprof can cause significant STW latencies in applications with a
lot of goroutines (> 1-10k), these latencies only occur if the profile
is requested - it doesn't cause a delay by simply being available.

The fgprof profile is mounted on
`http://localhost:6060/debug/fgprof?seconds=3`

Signed-off-by: Andrew Thornton <art27@cantab.net>

3 files changed, 7 insertions, 0 deletions

diff --git a/cmd/web.go b/cmd/web.go
index 8c7c02617..43bb0ada9 100644
--- a/cmd/web.go
+++ b/cmd/web.go
@@ -21,6 +21,7 @@ import (
 	"code.gitea.io/gitea/routers"
 	"code.gitea.io/gitea/routers/install"
 
+	"github.com/felixge/fgprof"
 	"github.com/urfave/cli"
 	ini "gopkg.in/ini.v1"
 )
@@ -145,6 +146,7 @@ func runWeb(ctx *cli.Context) error {
 
 	if setting.EnablePprof {
 		go func() {
+			http.DefaultServeMux.Handle("/debug/fgprof", fgprof.Handler())
 			_, _, finished := process.GetManager().AddTypedContext(context.Background(), "Web: PProf Server", process.SystemProcessType, true)
 			log.Info("Starting pprof server on localhost:6060")
 			log.Info("%v", http.ListenAndServe("localhost:6060", nil))
diff --git a/go.mod b/go.mod
index e7cb85ad1..e06ccfe13 100644
--- a/go.mod
+++ b/go.mod
@@ -26,6 +26,7 @@ require (
 	github.com/editorconfig/editorconfig-core-go/v2 v2.4.4
 	github.com/emirpasic/gods v1.18.1
 	github.com/ethantkoenig/rupture v1.0.1
+	github.com/felixge/fgprof v0.9.2
 	github.com/gliderlabs/ssh v0.3.4
 	github.com/go-chi/chi/v5 v5.0.7
 	github.com/go-chi/cors v1.2.1
diff --git a/go.sum b/go.sum
index d0a1cb84e..9c99adfbe 100644
--- a/go.sum
+++ b/go.sum
@@ -426,6 +426,8 @@ github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5Kwzbycv
 github.com/fatih/color v1.9.0/go.mod h1:eQcE1qtQxscV5RaZvpXrrb8Drkc3/DdQ+uUYCNjL+zU=
 github.com/fatih/color v1.13.0 h1:8LOYc1KYPPmyKMuN8QV2DNRWNbLo6LZ0iLs8+mlH53w=
 github.com/fatih/color v1.13.0/go.mod h1:kLAiJbzzSOZDVNGyDpeOxJ47H46qBXwg5ILebYFFOfk=
+github.com/felixge/fgprof v0.9.2 h1:tAMHtWMyl6E0BimjVbFt7fieU6FpjttsZN7j0wT5blc=
+github.com/felixge/fgprof v0.9.2/go.mod h1:+VNi+ZXtHIQ6wIw6bUT8nXQRefQflWECoFyRealT5sg=
 github.com/felixge/httpsnoop v1.0.1/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
 github.com/felixge/httpsnoop v1.0.2 h1:+nS9g82KMXccJ/wp0zyRW9ZBHFETmMGtkk+2CTTrW4o=
 github.com/felixge/httpsnoop v1.0.2/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
@@ -769,6 +771,7 @@ github.com/google/pprof v0.0.0-20210226084205-cbba55b83ad5/go.mod h1:kpwsk12EmLe
 github.com/google/pprof v0.0.0-20210601050228-01bbb1931b22/go.mod h1:kpwsk12EmLew5upagYY7GY0pfYCcupk39gWOCRROcvE=
 github.com/google/pprof v0.0.0-20210609004039-a478d1d731e9/go.mod h1:kpwsk12EmLew5upagYY7GY0pfYCcupk39gWOCRROcvE=
 github.com/google/pprof v0.0.0-20210720184732-4bb14d4b1be1/go.mod h1:kpwsk12EmLew5upagYY7GY0pfYCcupk39gWOCRROcvE=
+github.com/google/pprof v0.0.0-20211214055906-6f57359322fd/go.mod h1:KgnwoLYCZ8IQu3XUZ8Nc/bM9CCZFOyjUNOSygVozoDg=
 github.com/google/pprof v0.0.0-20220509035851-59ca7ad80af3 h1:vFrXU7L2gqtlP/ZGijSpaDIc16ZQrZI4FAuYtpQTyQc=
 github.com/google/pprof v0.0.0-20220509035851-59ca7ad80af3/go.mod h1:Pt31oes+eGImORns3McJn8zHefuQl2rG8l6xQjGYB4U=
 github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
@@ -892,6 +895,7 @@ github.com/iancoleman/strcase v0.0.0-20180726023541-3605ed457bf7/go.mod h1:SK73t
 github.com/iancoleman/strcase v0.2.0/go.mod h1:iwCmte+B7n89clKwxIoIXy/HfoL7AsD47ZCWhYzw7ho=
 github.com/ianlancetaylor/demangle v0.0.0-20181102032728-5e5cf60278f6/go.mod h1:aSSvb/t6k1mPoxDqO4vJh6VOCGPwU4O0C2/Eqndh1Sc=
 github.com/ianlancetaylor/demangle v0.0.0-20200824232613-28f6c0f3b639/go.mod h1:aSSvb/t6k1mPoxDqO4vJh6VOCGPwU4O0C2/Eqndh1Sc=
+github.com/ianlancetaylor/demangle v0.0.0-20210905161508-09a460cdf81d/go.mod h1:aYm2/VgdVmcIU8iMfdMvDMsRAQjcfZSKFby6HOFvi/w=
 github.com/imdario/mergo v0.3.4/go.mod h1:2EnlNZ0deacrJVfApfmtdGgDfMuh/nq6Ok1EcJh5FfA=
 github.com/imdario/mergo v0.3.8/go.mod h1:2EnlNZ0deacrJVfApfmtdGgDfMuh/nq6Ok1EcJh5FfA=
 github.com/imdario/mergo v0.3.9/go.mod h1:2EnlNZ0deacrJVfApfmtdGgDfMuh/nq6Ok1EcJh5FfA=