Lock free skiplist with size (#99)

Add skiplist with generalized size computation

---------

Co-authored-by: Carine Morel <[email protected]>, Sooraj Srinivasan <[email protected]>

Author: polytypic

bench/bench_skiplist.ml

@@ -0,0 +1,57 @@
+open Saturn
+
+let workload num_elems num_threads add remove =
+  let sl = Skiplist.create ~compare:Int.compare () in
+  let elems = Array.init num_elems (fun _ -> Random.int 10000) in
+  let push () =
+    Domain.spawn (fun () ->
+        let start_time = Unix.gettimeofday () in
+        for i = 0 to (num_elems - 1) / num_threads do
+          Domain.cpu_relax ();
+          let prob = Random.float 1.0 in
+          if prob < add then Skiplist.try_add sl (Random.int 10000) () |> ignore
+          else if prob >= add && prob < add +. remove then
+            Skiplist.try_remove sl (Random.int 10000) |> ignore
+          else Skiplist.mem sl elems.(i) |> ignore
+        done;
+        start_time)
+  in
+  let threads = List.init num_threads (fun _ -> push ()) in
+  let start_time_threads =
+    List.map (fun domain -> Domain.join domain) threads
+  in
+  let end_time = Unix.gettimeofday () in
+  let time_diff = end_time -. List.nth start_time_threads 0 in
+  time_diff
+
+(* A write heavy workload with threads with 50% adds and 50% removes. *)
+let write_heavy_workload num_elems num_threads =
+  workload num_elems num_threads 0.5 0.5
+
+(* A regular workload with 90% reads, 9% adds and 1% removes. *)
+let read_heavy_workload num_elems num_threads =
+  workload num_elems num_threads 0.09 0.01
+
+let moderate_heavy_workload num_elems num_threads =
+  workload num_elems num_threads 0.2 0.1
+
+let balanced_heavy_workload num_elems num_threads =
+  workload num_elems num_threads 0.3 0.2
+
+let bench ~workload_type ~num_elems ~num_threads () =
+  let workload =
+    if workload_type = "read_heavy" then read_heavy_workload
+    else if workload_type = "moderate_heavy" then moderate_heavy_workload
+    else if workload_type = "balanced_heavy" then balanced_heavy_workload
+    else write_heavy_workload
+  in
+  let results = ref [] in
+  for i = 1 to 10 do
+    let time = workload num_elems num_threads in
+    if i > 1 then results := time :: !results
+  done;
+  let results = List.sort Float.compare !results in
+  let median_time = List.nth results 4 in
+  let median_throughput = Float.of_int num_elems /. median_time in
+  Benchmark_result.create_generic ~median_time ~median_throughput
+    ("atomic_skiplist_" ^ workload_type)

bench/main.ml

@@ -7,6 +7,10 @@ let benchmark_list =
     Mpmc_queue.bench ~use_cas:true ~takers:4 ~pushers:4;
     Mpmc_queue.bench ~use_cas:true ~takers:1 ~pushers:8;
     Mpmc_queue.bench ~use_cas:true ~takers:8 ~pushers:1;
+    Bench_skiplist.bench ~workload_type:"read_heavy" ~num_elems:2000000
+      ~num_threads:2;
+    Bench_skiplist.bench ~workload_type:"moderate_heavy" ~num_elems:2000000
+      ~num_threads:2;
   ]
 
 let () =

src/saturn.ml

@@ -35,3 +35,4 @@ module Single_prod_single_cons_queue =
 
 module Single_consumer_queue = Saturn_lockfree.Single_consumer_queue
 module Relaxed_queue = Mpmc_relaxed_queue
+module Skiplist = Saturn_lockfree.Skiplist

src/saturn.mli

@@ -39,3 +39,4 @@ module Single_prod_single_cons_queue =
 
 module Single_consumer_queue = Saturn_lockfree.Single_consumer_queue
 module Relaxed_queue = Mpmc_relaxed_queue
+module Skiplist = Saturn_lockfree.Skiplist

src_lockfree/saturn_lockfree.ml

@@ -33,3 +33,4 @@ module Single_prod_single_cons_queue = Spsc_queue
 module Single_consumer_queue = Mpsc_queue
 module Relaxed_queue = Mpmc_relaxed_queue
 module Size = Size
+module Skiplist = Skiplist

src_lockfree/saturn_lockfree.mli

@@ -36,4 +36,5 @@ module Work_stealing_deque = Ws_deque
 module Single_prod_single_cons_queue = Spsc_queue
 module Single_consumer_queue = Mpsc_queue
 module Relaxed_queue = Mpmc_relaxed_queue
+module Skiplist = Skiplist
 module Size = Size