13647: Use cluster config instead of custom keepstore config.

[arvados.git] / sdk / go / httpserver / request_limiter.go

diff --git a/sdk/go/httpserver/request_limiter.go b/sdk/go/httpserver/request_limiter.go
index 178ffb90f4facbebdfd6809bb1448e84904bc82f..23e6e016d303bbc78abefcc39bfa0fb65b8ef0fe 100644 (file)
--- 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: