Update from Thomas's comment

Author: moyodiallo

service/pool.ml

@@ -6,9 +6,7 @@ type ('request, 'reply) t = {
 
 let rec run_worker t handle =
   let request, set_reply = Eio.Stream.take t.requests in
-  Atomic.incr t.running;
   handle request |> Promise.resolve set_reply;
-  Atomic.decr t.running;
   run_worker t handle
 
 let create ~sw ~domain_mgr ~n_workers handle =
@@ -25,6 +23,6 @@ let use t request =
   Eio.Stream.add t.requests (request, set_reply);
   Promise.await reply
 
-let running_workers t = Atomic.get t.running
-
 let n_workers t = t.n_workers
+
+let wait_requests t = Eio.Stream.length t.requests

service/solver.ml

@@ -12,6 +12,7 @@ type t = {
 
 let ocaml = OpamPackage.Name.of_string "ocaml"
 
+
 module Metrics = struct
   open Prometheus
 
@@ -26,13 +27,13 @@ module Metrics = struct
     let help = "Number of handled requests by state" in
     Gauge.v_label ~label_name:"state" ~help ~namespace ~subsystem "solve_request_state"
 
-  let update_request_handling pool =
-    let running = Pool.running_workers pool in
-    let waiting = (Pool.n_workers pool) - running in
+  let update_request_handling pool n_requests =
+    let workers = Pool.n_workers pool in
+    let waiting = Pool.wait_requests pool in
+    let running = min !n_requests workers in
     Gauge.set (request_handling "running") (float_of_int running);
     Gauge.set (request_handling "waiting") (float_of_int waiting)
 
-
   let request_ok =
     let help = "Total number of success solve requests" in
     Counter.v ~help ~namespace ~subsystem "success_solve"
@@ -160,14 +161,16 @@ let solve ?cancelled t ~log request =
   Log.info log "Solving for %a" Fmt.(list ~sep:comma string) root_pkgs;
   let serious_errors = ref [] in
   let cancels_without_running = ref 0 in
+  let n_requests = ref 0 in
   let*! root_pkgs = parse_opams request.root_pkgs in
   let*! pinned_pkgs = parse_opams request.pinned_pkgs in
   let*! packages = Stores.packages t.stores opam_repository_commits in
   let results =
     platforms
     |> Fiber.List.map (fun (id, vars) ->
         Prometheus.Counter.inc_one Metrics.request_handling_total;
-        Metrics.update_request_handling t.pool;
+        incr n_requests;
+        Metrics.update_request_handling t.pool n_requests;
         let result =
           solve_for_platform t id
             ?cancelled
@@ -179,7 +182,8 @@ let solve ?cancelled t ~log request =
             ~pins
             ~vars
         in
-        Metrics.update_request_handling t.pool;
+        decr n_requests;
+        Metrics.update_request_handling t.pool n_requests;
         (id, result)
       )
     |> List.filter_map (fun (id, result) ->