From d56e938b939e05a35b23e9090883303e28ee7745 Mon Sep 17 00:00:00 2001
From: Daniele Cattaneo <daniele3.cattaneo@mail.polimi.it>
Date: Sat, 8 Apr 2023 21:25:07 +0200
Subject: [PATCH] Add semaphore synchronization primitive.
Signed-off-by: Terraneo Federico <fede.tft@miosix.org>
---
miosix/kernel/kernel.h | 2 +
miosix/kernel/sync.cpp | 113 ++++++++++++++++++++++++++++++++++++++++-
miosix/kernel/sync.h | 105 ++++++++++++++++++++++++++++++++++++++
3 files changed, 218 insertions(+), 2 deletions(-)
diff --git a/miosix/kernel/kernel.h b/miosix/kernel/kernel.h
index 59ee7b83..72b62990 100755
--- a/miosix/kernel/kernel.h
+++ b/miosix/kernel/kernel.h
@@ -1052,6 +1052,8 @@ private:
friend class Mutex;
//Needs access to flags
friend class ConditionVariable;
+ //Needs access to flags
+ friend class Semaphore;
//Needs access to flags, schedData
friend class PriorityScheduler;
//Needs access to flags, schedData
diff --git a/miosix/kernel/sync.cpp b/miosix/kernel/sync.cpp
index 90fce52b..90f58212 100644
--- a/miosix/kernel/sync.cpp
+++ b/miosix/kernel/sync.cpp
@@ -410,7 +410,7 @@ TimedWaitResult ConditionVariable::timedWait(Mutex& m, long long absTime)
//Disallow absolute sleeps with negative or too low values, as the ns2tick()
//algorithm in TimeConversion can't handle negative values and may undeflow
//even with very low values due to a negative adjustOffsetNs. As an unlikely
- //side effect, very shor sleeps done very early at boot will be extended.
+ //side effect, very short sleeps done very early at boot will be extended.
absTime=std::max(absTime,100000LL);
PauseKernelLock dLock;
@@ -451,7 +451,7 @@ TimedWaitResult ConditionVariable::timedWait(pthread_mutex_t *m, long long absTi
//Disallow absolute sleeps with negative or too low values, as the ns2tick()
//algorithm in TimeConversion can't handle negative values and may undeflow
//even with very low values due to a negative adjustOffsetNs. As an unlikely
- //side effect, very shor sleeps done very early at boot will be extended.
+ //side effect, very short sleeps done very early at boot will be extended.
absTime=std::max(absTime,100000LL);
FastInterruptDisableLock dLock;
Thread *t=Thread::IRQgetCurrentThread();
@@ -525,4 +525,113 @@ void ConditionVariable::broadcast()
if(hppw) Thread::yield();
}
+//
+// class Semaphore
+//
+
+Thread *Semaphore::IRQsignalNoPreempt()
+{
+ //Check if somebody is waiting
+ if(fifo.empty())
+ {
+ //Nobody there, just increment the counter
+ count++;
+ return nullptr;
+ }
+ CondData *cd=fifo.front();
+ Thread *t=cd->thread;
+ fifo.pop_front();
+ t->flags.IRQsetCondWait(false);
+ t->flags.IRQsetSleep(false); //Needed due to timedwait
+ return t;
+}
+
+void Semaphore::IRQsignal()
+{
+ //Update the state of the FIFO and the counter
+ Thread *t=IRQsignalNoPreempt();
+ if(t==nullptr) return;
+ //If the woken thread has higher priority trigger a reschedule
+ if(Thread::IRQgetCurrentThread()->IRQgetPriority()<t->IRQgetPriority())
+ Scheduler::IRQfindNextThread();
+}
+
+void Semaphore::signal()
+{
+ bool hppw=false;
+ {
+ //Global interrupt lock because Semaphore is IRQ-safe
+ FastInterruptDisableLock dLock;
+ //Update the state of the FIFO and the counter
+ Thread *t=IRQsignalNoPreempt();
+ if(t)
+ {
+ //If the woken thread has higher priority trigger a yield
+ if(Thread::IRQgetCurrentThread()->IRQgetPriority()<t->IRQgetPriority())
+ hppw=true;
+ }
+ }
+ if(hppw) Thread::yield();
+}
+
+void Semaphore::wait()
+{
+ //Global interrupt lock because Semaphore is IRQ-safe
+ FastInterruptDisableLock dLock;
+ //If the counter is positive, decrement it and we're done
+ if(count>0)
+ {
+ count--;
+ return;
+ }
+ //Otherwise put ourselves in queue and wait
+ Thread *t=Thread::getCurrentThread();
+ CondData listItem(t);
+ fifo.push_back(&listItem); //Add entry to tail of list
+ t->flags.IRQsetCondWait(true);
+ {
+ FastInterruptEnableLock eLock(dLock);
+ //The wait becomes effective here
+ Thread::yield();
+ }
+}
+
+TimedWaitResult Semaphore::timedWait(long long absTime)
+{
+ //Disallow absolute sleeps with negative or too low values, as the ns2tick()
+ //algorithm in TimeConversion can't handle negative values and may undeflow
+ //even with very low values due to a negative adjustOffsetNs. As an unlikely
+ //side effect, very short sleeps done very early at boot will be extended.
+ absTime=std::max(absTime,100000LL);
+
+ //Global interrupt lock because Semaphore is IRQ-safe
+ FastInterruptDisableLock dLock;
+ //If the counter is positive, decrement it and we're done
+ if(count>0)
+ {
+ count--;
+ return TimedWaitResult::NoTimeout;
+ }
+ //Otherwise put ourselves in queue...
+ Thread *t=Thread::getCurrentThread();
+ CondData listItem(t);
+ fifo.push_back(&listItem);
+ //...and simultaneously to sleep
+ SleepData sleepData(t,absTime);
+ IRQaddToSleepingList(&sleepData);
+ t->flags.IRQsetCondWait(true);
+ {
+ FastInterruptEnableLock eLock(dLock);
+ //Wait/sleep becomes effective here
+ Thread::yield();
+ }
+
+ //We got woken up by either the sleep or the wait. Ensure that the thread
+ //is removed from both the wait list and the sleep list.
+ bool removed=fifo.removeFast(&listItem);
+ IRQremoveFromSleepingList(&sleepData);
+ //If we were still in the fifo, we were woken up by a timeout
+ return removed ? TimedWaitResult::Timeout : TimedWaitResult::NoTimeout;
+}
+
} //namespace miosix
diff --git a/miosix/kernel/sync.h b/miosix/kernel/sync.h
index 626846ae..972d0af7 100644
--- a/miosix/kernel/sync.h
+++ b/miosix/kernel/sync.h
@@ -1,5 +1,6 @@
/***************************************************************************
* Copyright (C) 2008-2023 by Terraneo Federico *
+ * Copyright (C) 2023 by Daniele Cattaneo *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
@@ -532,6 +533,110 @@ private:
IntrusiveList<CondData> condList;
};
+/**
+ * Semaphore primitive for syncronization between multiple threads and
+ * optionally an interrupt handler.
+ *
+ * A semaphore is an integer counter that represents the availability of one
+ * or more items of a resource. A producer thread can signal the semaphore to
+ * increment the counter, making more items available. A consumer thread can
+ * wait for the availability of at least one item (i.e. for the counter to be
+ * positive) by performing a `wait' on the semaphore. If the counter is already
+ * positive, wait decrements the counter and terminates immediately. Otherwise
+ * it waits for a `signal' to increment the counter first.
+ *
+ * It is possible to use Semaphores to orchestrate communication between IRQ
+ * handlers and the main driver code by using the APIs prefixed by `IRQ'.
+ *
+ * \note As with all other synchronization primitives, Semaphores are inherently
+ * shared between multiple threads, therefore special care must be taken in
+ * managing their lifetime and ownership.
+ * \since Miosix 2.5
+ */
+class Semaphore
+{
+public:
+ /**
+ * Initialize a new semaphore.
+ * \param initialCount The initial value of the counter.
+ */
+ Semaphore(unsigned int initialCount=0) : count(initialCount) {}
+
+ /**
+ * Increment the semaphore counter, waking up at most one waiting thread.
+ * Only for use in IRQ handlers.
+ * \warning Use in a thread context with interrupts disabled or with the
+ * kernel paused is forbidden.
+ */
+ void IRQsignal();
+
+ /**
+ * Increment the semaphore counter, waking up at most one waiting thread.
+ */
+ void signal();
+
+ /**
+ * Wait for the semaphore counter to be positive, and then decrement it.
+ */
+ void wait();
+
+ /**
+ * Wait up to a given timeout for the semaphore counter to be positive,
+ * and then decrement it.
+ * \param absTime absolute timeout time in nanoseconds
+ * \return whether the return was due to a timeout or wakeup
+ */
+ TimedWaitResult timedWait(long long absTime);
+
+ /**
+ * Decrement the counter only if it is positive. Only for use in IRQ
+ * handlers or with interrupts disabled.
+ * \return true if the counter was positive.
+ */
+ inline bool IRQtryWait()
+ {
+ // Check if the counter is positive
+ if(count>0)
+ {
+ // The wait "succeeded"
+ count--;
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Decrement the counter only if it is positive.
+ * \return true if the counter was positive.
+ */
+ bool tryWait()
+ {
+ // Global interrupt lock because Semaphore is IRQ-safe
+ FastInterruptDisableLock dLock;
+ return IRQtryWait();
+ }
+
+ /**
+ * \return the current semaphore counter.
+ */
+ unsigned int getCount() { return count; }
+
+private:
+ // Disallow copies
+ Semaphore(const Semaphore&) = delete;
+ Semaphore& operator= (const Semaphore&) = delete;
+
+ /**
+ * \internal
+ * Internal method that signals the semaphore without triggering a
+ * rescheduling for prioritizing newly-woken threads.
+ */
+ inline Thread *IRQsignalNoPreempt();
+
+ volatile unsigned int count; ///< Counter of the semaphore
+ IntrusiveList<CondData> fifo; ///< List of waiting threads
+};
+
/**
* \}
*/
--
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