X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/0dc0c5650ddcd8376aea84d32d2b81b1cdba0946..f04693da1811e670d4cbb981debeecf14d79137c:/sdk/go/httpserver/request_limiter.go

diff --git a/sdk/go/httpserver/request_limiter.go b/sdk/go/httpserver/request_limiter.go
index 178ffb90f4..23e6e016d3 100644
--- a/sdk/go/httpserver/request_limiter.go
+++ b/sdk/go/httpserver/request_limiter.go
@@ -1,22 +1,84 @@
+// Copyright (C) The Arvados Authors. All rights reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+
 package httpserver
 
 import (
 	"net/http"
+	"sync/atomic"
+
+	"github.com/prometheus/client_golang/prometheus"
 )
 
+// RequestCounter is an http.Handler that tracks the number of
+// requests in progress.
+type RequestCounter interface {
+	http.Handler
+
+	// Current() returns the number of requests in progress.
+	Current() int
+
+	// Max() returns the maximum number of concurrent requests
+	// that will be accepted.
+	Max() int
+}
+
 type limiterHandler struct {
 	requests chan struct{}
 	handler  http.Handler
+	count    int64 // only used if cap(requests)==0
 }
 
-func NewRequestLimiter(maxRequests int, handler http.Handler) http.Handler {
-	return &limiterHandler{
+// NewRequestLimiter returns a RequestCounter that delegates up to
+// maxRequests at a time to the given handler, and responds 503 to all
+// incoming requests beyond that limit.
+//
+// "concurrent_requests" and "max_concurrent_requests" metrics are
+// registered with the given reg, if reg is not nil.
+func NewRequestLimiter(maxRequests int, handler http.Handler, reg *prometheus.Registry) RequestCounter {
+	h := &limiterHandler{
 		requests: make(chan struct{}, maxRequests),
 		handler:  handler,
 	}
+	if reg != nil {
+		reg.MustRegister(prometheus.NewGaugeFunc(
+			prometheus.GaugeOpts{
+				Namespace: "arvados",
+				Name:      "concurrent_requests",
+				Help:      "Number of requests in progress",
+			},
+			func() float64 { return float64(h.Current()) },
+		))
+		reg.MustRegister(prometheus.NewGaugeFunc(
+			prometheus.GaugeOpts{
+				Namespace: "arvados",
+				Name:      "max_concurrent_requests",
+				Help:      "Maximum number of concurrent requests",
+			},
+			func() float64 { return float64(h.Max()) },
+		))
+	}
+	return h
+}
+
+func (h *limiterHandler) Current() int {
+	if cap(h.requests) == 0 {
+		return int(atomic.LoadInt64(&h.count))
+	}
+	return len(h.requests)
+}
+
+func (h *limiterHandler) Max() int {
+	return cap(h.requests)
 }
 
 func (h *limiterHandler) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
+	if cap(h.requests) == 0 {
+		atomic.AddInt64(&h.count, 1)
+		h.handler.ServeHTTP(resp, req)
+		atomic.AddInt64(&h.count, -1)
+	}
 	select {
 	case h.requests <- struct{}{}:
 	default: