From 9aab33c2e99e8dc134fdb7029c257c0c31649f84 Mon Sep 17 00:00:00 2001
From: Terraneo Federico <fede.tft@miosix.org>
Date: Thu, 27 Apr 2023 01:04:51 +0200
Subject: [PATCH] Prevent spurious wakeup in Semaphore
---
miosix/kernel/sync.cpp | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/miosix/kernel/sync.cpp b/miosix/kernel/sync.cpp
index 5d66ed60..b7cc79b9 100644
--- a/miosix/kernel/sync.cpp
+++ b/miosix/kernel/sync.cpp
@@ -454,6 +454,7 @@ Thread *Semaphore::IRQsignalNoPreempt()
}
WaitToken *cd=fifo.front();
Thread *t=cd->thread;
+ cd->thread=nullptr; //Thread pointer doubles as flag against spurious wakeup
fifo.pop_front();
t->IRQwakeup();
return t;
@@ -500,8 +501,8 @@ void Semaphore::wait()
//Otherwise put ourselves in queue and wait
WaitToken listItem(Thread::IRQgetCurrentThread());
fifo.push_back(&listItem); //Add entry to tail of list
- Thread::IRQenableIrqAndWait(dLock);
- fifo.removeFast(&listItem); //In case of spurious wakeup
+ while(listItem.thread) Thread::IRQenableIrqAndWait(dLock);
+ //Spurious wakeup handled by while loop, listItem already removed from fifo
}
TimedWaitResult Semaphore::timedWait(long long absTime)
@@ -517,9 +518,15 @@ TimedWaitResult Semaphore::timedWait(long long absTime)
//Otherwise put ourselves in queue and wait
WaitToken listItem(Thread::IRQgetCurrentThread());
fifo.push_back(&listItem); //Add entry to tail of list
- auto result=Thread::IRQenableIrqAndTimedWait(dLock,absTime);
- fifo.removeFast(&listItem); //In case of timeout or spurious wakeup
- return result;
+ while(listItem.thread)
+ {
+ if(Thread::IRQenableIrqAndTimedWait(dLock,absTime)==TimedWaitResult::Timeout)
+ {
+ fifo.removeFast(&listItem); //Remove fifo entry in case of timeout
+ return TimedWaitResult::Timeout;
+ }
+ }
+ return TimedWaitResult::NoTimeout;
}
} //namespace miosix
--
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