From 464f6ec4163ce647ab3dd7495bf0a5d0222dc99c Mon Sep 17 00:00:00 2001
From: Igor Matuszewski <xanewok@gmail.com>
Date: Mon, 16 Mar 2026 21:49:36 +0100
Subject: [PATCH] Make watchdog suppression counter-based for safe nesting

Change WatchdogSuppressionGuard from AtomicBool to AtomicUsize so
multiple guards can be active simultaneously. The watchdog resumes
only when all guards have been dropped (counter reaches 0).

This allows placing suppress_watchdog() inside node constructors
without worrying about interleaving with test-level suppression.
---
 msim/src/sim/runtime/mod.rs | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/msim/src/sim/runtime/mod.rs b/msim/src/sim/runtime/mod.rs
index 5ca5ab4..1634923 100644
--- a/msim/src/sim/runtime/mod.rs
+++ b/msim/src/sim/runtime/mod.rs
@@ -8,7 +8,7 @@ use std::{
     io::Write,
     net::IpAddr,
     sync::{
-        atomic::{AtomicBool, Ordering},
+        atomic::{AtomicUsize, Ordering},
         Arc, Mutex, RwLock,
     },
     time::Duration,
@@ -75,7 +75,7 @@ impl Runtime {
             task: task.handle().clone(),
             sims: Default::default(),
             config,
-            watchdog_suppressed: Arc::new(AtomicBool::new(false)),
+            watchdog_suppressed: Arc::new(AtomicUsize::new(0)),
         };
         let rt = Runtime { rand, task, handle };
         rt.add_simulator::<fs::FsSim>();
@@ -298,7 +298,7 @@ pub struct Handle {
     pub(crate) task: task::TaskHandle,
     pub(crate) sims: Arc<Mutex<HashMap<TypeId, Arc<dyn plugin::Simulator>>>>,
     pub(crate) config: SimConfig,
-    watchdog_suppressed: Arc<AtomicBool>,
+    watchdog_suppressed: Arc<AtomicUsize>,
 }
 
 impl Handle {
@@ -385,26 +385,29 @@ impl Handle {
     /// simulator may take a long time to drain ready tasks without advancing
     /// simulated time.
     pub fn suppress_watchdog(&self) -> WatchdogSuppressionGuard {
-        self.watchdog_suppressed.store(true, Ordering::Relaxed);
+        self.watchdog_suppressed.fetch_add(1, Ordering::Relaxed);
         WatchdogSuppressionGuard {
-            flag: Arc::clone(&self.watchdog_suppressed),
+            counter: Arc::clone(&self.watchdog_suppressed),
         }
     }
 
     /// Check whether the watchdog is currently suppressed.
     pub(crate) fn is_watchdog_suppressed(&self) -> bool {
-        self.watchdog_suppressed.load(Ordering::Relaxed)
+        self.watchdog_suppressed.load(Ordering::Relaxed) > 0
     }
 }
 
 /// RAII guard that re-enables the watchdog when dropped.
+///
+/// Multiple guards can be active simultaneously (e.g. from nested calls);
+/// the watchdog resumes only when all guards have been dropped.
 pub struct WatchdogSuppressionGuard {
-    flag: Arc<AtomicBool>,
+    counter: Arc<AtomicUsize>,
 }
 
 impl Drop for WatchdogSuppressionGuard {
     fn drop(&mut self) {
-        self.flag.store(false, Ordering::Relaxed);
+        self.counter.fetch_sub(1, Ordering::Relaxed);
     }
 }