From 3b5d6d93a501d6e9cd649c51dfdb08361be83412 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20L=C3=B3pez?=
 <2642849+elopez@users.noreply.github.com>
Date: Tue, 16 Jul 2024 14:08:19 +0200
Subject: [PATCH] Raise default number of workers (#1288)

Now the default number of workers will be equal to the number
of cores on the system, with a minimum of 1 and a maximum of 4.
---
 lib/Echidna/Types/Campaign.hs     | 11 ++++++++---
 tests/solidity/basic/default.yaml |  4 ++--
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/Echidna/Types/Campaign.hs b/lib/Echidna/Types/Campaign.hs
index 78a885189..b54c19185 100644
--- a/lib/Echidna/Types/Campaign.hs
+++ b/lib/Echidna/Types/Campaign.hs
@@ -3,10 +3,10 @@ module Echidna.Types.Campaign where
 import Control.Concurrent (ThreadId)
 import Data.Aeson
 import Data.Map (Map)
-import Data.Maybe (fromMaybe)
 import Data.Text (Text)
 import Data.Text qualified as T
 import Data.Word (Word8, Word16)
+import GHC.Conc (numCapabilities)
 
 import Echidna.ABI (GenDict, emptyDict, encodeSig)
 import Echidna.Types
@@ -211,9 +211,14 @@ defaultSymExecAskSMTIters :: Integer
 defaultSymExecAskSMTIters = 1
 
 -- | Get number of fuzzing workers (doesn't include sym exec worker)
--- Defaults to 1 if set to Nothing
+-- Defaults to `N` if set to Nothing, where `N` is Haskell's -N value,
+-- usually the number of cores, clamped between 1 and 4.
 getNFuzzWorkers :: CampaignConf -> Int
-getNFuzzWorkers conf = fromIntegral (fromMaybe 1 (conf.workers))
+getNFuzzWorkers conf = maybe defaultN fromIntegral conf.workers
+  where
+    n = numCapabilities
+    maxN = max 1 n
+    defaultN = min 4 maxN -- capped at 4 by default
 
 -- | Number of workers, including SymExec worker if there is one
 getNWorkers :: CampaignConf -> Int
diff --git a/tests/solidity/basic/default.yaml b/tests/solidity/basic/default.yaml
index d9c277287..fc52ab1cc 100644
--- a/tests/solidity/basic/default.yaml
+++ b/tests/solidity/basic/default.yaml
@@ -89,8 +89,8 @@ rpcUrl: null
 rpcBlock: null
 # Etherscan API key
 etherscanApiKey: null
-# number of workers
-workers: 1
+# number of workers. By default (unset) its value is the clamp of the number cores between 1 and 4
+workers: null
 # events server port
 server: null
 # whether to add an additional symbolic execution worker