os-semaphore.cpp

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/*
 * This file is part of the µOS++ project (https://micro-os-plus.github.io/).
 * Copyright (c) 2016-2025 Liviu Ionescu. All rights reserved.
 *
 * Permission to use, copy, modify, and/or distribute this software
 * for any purpose is hereby granted, under the terms of the MIT license.
 *
 * If a copy of the license was not distributed with this file, it can
 * be obtained from https://opensource.org/licenses/mit.
 */
 
#if defined(OS_USE_OS_APP_CONFIG_H)
#include <cmsis-plus/os-app-config.h>
#endif
 
#include <cmsis-plus/rtos/os.h>
 
// ----------------------------------------------------------------------------
 
#if defined(__clang__)
#pragma clang diagnostic ignored "-Wc++98-compat"
#endif
 
// ----------------------------------------------------------------------------
 
namespace os
{
  namespace rtos
  {
    // ------------------------------------------------------------------------
 
    const semaphore::attributes_binary semaphore::initializer_binary{ 0 };
 
    // ------------------------------------------------------------------------
 
    semaphore::semaphore (const char* name, const attributes& attr)
        : semaphore{ name, attr.sm_max_value, attr.sm_initial_value, attr }
    {
    }
 
    semaphore::semaphore (const char* name, const count_t max_value,
                          const count_t initial_value,
                          const attributes& attr
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
                          __attribute__ ((unused))
#endif
                          )
        : object_named_system{ name }, //
          max_value_ (max_value), //
          initial_value_ (initial_value)
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s %u %u\n", __func__, this, this->name (),
                     initial_value, max_value_);
#endif
 
      // Don't call this from interrupt handlers.
      os_assert_throw (!interrupts::in_handler_mode (), EPERM);
 
      // The CMSIS validator requires the max_value to be equal to
      // the initial count, which can be 0, but we patch it on the way.
      assert (max_value_ > 0);
      assert (initial_value >= 0);
      assert (initial_value <= max_value_);
 
      count_ = initial_value;
 
#if !defined(OS_USE_RTOS_PORT_SEMAPHORE)
      clock_ = attr.clock != nullptr ? attr.clock : &sysclock;
#endif
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      port::semaphore::create (this);
 
#else
 
      internal_init_ ();
 
#endif
    }
 
    semaphore::~semaphore ()
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s\n", __func__, this, name ());
#endif
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      port::semaphore::destroy (this);
 
#else
 
      // There must be no threads waiting for this semaphore.
      assert (list_.empty ());
 
#endif
    }
 
    void
    semaphore::internal_init_ (void)
    {
 
      count_ = initial_value_;
 
#if !defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      // Wake-up all threads, if any.
      // Need not be inside the critical section,
      // the list is protected by inner `resume_one()`.
      list_.resume_all ();
 
#endif /* !defined(OS_USE_RTOS_PORT_SEMAPHORE) */
    }
 
    /*
     * Internal function.
     * Should be called from an interrupts critical section.
     */
    bool
    semaphore::internal_try_wait_ (void)
    {
      if (count_ > 0)
        {
#pragma GCC diagnostic push
#if defined(__clang__)
#pragma clang diagnostic ignored "-Wdeprecated-volatile"
#elif defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wvolatile"
#endif
          --count_;
#pragma GCC diagnostic pop
 
#if defined(OS_TRACE_RTOS_SEMAPHORE)
          trace::printf ("%s() @%p %s >%u\n", __func__, this, name (), count_);
#endif
          return true;
        }
 
        // Count may be 0.
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s false\n", __func__, this, name ());
#endif
      return false;
    }
 
    result_t
    semaphore::post (void)
    {
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s\n", __func__, this, name ());
#endif
 
      return port::semaphore::post (this);
 
#else
 
      // Don't call this from high priority interrupts.
      assert (port::interrupts::is_priority_valid ());
 
      {
        // ----- Enter critical section ---------------------------------------
        interrupts::critical_section ics;
 
        if (count_ >= this->max_value_)
          {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
            trace::printf ("%s() @%p %s EAGAIN\n", __func__, this, name ());
#endif
            return EAGAIN;
          }
 
#pragma GCC diagnostic push
#if defined(__clang__)
#pragma clang diagnostic ignored "-Wdeprecated-volatile"
#elif defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wvolatile"
#endif
        ++count_;
#pragma GCC diagnostic pop
 
#if defined(OS_TRACE_RTOS_SEMAPHORE)
        trace::printf ("%s() @%p %s count %u\n", __func__, this, name (),
                       count_);
#endif
        // ----- Exit critical section ----------------------------------------
      }
 
      // Wake-up one thread.
      list_.resume_one ();
 
      return result::ok;
 
#endif
    }
 
    result_t
    semaphore::wait ()
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s <%u\n", __func__, this, name (), count_);
#endif
 
      // Don't call this from interrupt handlers.
      os_assert_err (!interrupts::in_handler_mode (), EPERM);
      // Don't call this from critical regions.
      os_assert_err (!scheduler::locked (), EPERM);
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      return port::semaphore::wait (this);
 
#else
 
      // Extra test before entering the loop, with its inherent weight.
      // Trade size for speed.
      {
        // ----- Enter critical section ---------------------------------------
        interrupts::critical_section ics;
 
        if (internal_try_wait_ ())
          {
            return result::ok;
          }
        // ----- Exit critical section ----------------------------------------
      }
 
      thread& crt_thread = this_thread::thread ();
 
      // Prepare a list node pointing to the current thread.
      // Do not worry for being on stack, it is temporarily linked to the
      // list and guaranteed to be removed before this function returns.
      internal::waiting_thread_node node{ crt_thread };
 
      for (;;)
        {
          {
            // ----- Enter critical section -----------------------------------
            interrupts::critical_section ics;
 
            if (internal_try_wait_ ())
              {
                return result::ok;
              }
 
            // Add this thread to the semaphore waiting list.
            scheduler::internal_link_node (list_, node);
            // state::suspended set in above link().
            // ----- Exit critical section ------------------------------------
          }
 
          port::scheduler::reschedule ();
 
          // Remove the thread from the semaphore waiting list,
          // if not already removed by post().
          scheduler::internal_unlink_node (node);
 
          if (crt_thread.interrupted ())
            {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
              trace::printf ("%s() EINTR @%p %s\n", __func__, this, name ());
#endif
              return EINTR;
            }
        }
 
      /* NOTREACHED */
      return ENOTRECOVERABLE;
 
#endif
    }
 
    result_t
    semaphore::try_wait ()
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s <%u\n", __func__, this, name (), count_);
#endif
 
      // Don't call this from high priority interrupts.
      assert (port::interrupts::is_priority_valid ());
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      return port::semaphore::try_wait (this);
 
#else
 
      {
        // ----- Enter critical section ---------------------------------------
        interrupts::critical_section ics;
 
        if (internal_try_wait_ ())
          {
            return result::ok;
          }
        else
          {
            return EWOULDBLOCK;
          }
        // ----- Exit critical section ----------------------------------------
      }
 
#endif
    }
 
    result_t
    semaphore::timed_wait (clock::duration_t timeout)
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
#pragma GCC diagnostic push
#if defined(__clang__)
#elif defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wuseless-cast"
#endif
      trace::printf ("%s(%u) @%p %s <%u\n", __func__,
                     static_cast<unsigned int> (timeout), this, name (),
                     count_);
#pragma GCC diagnostic pop
#endif
 
      // Don't call this from interrupt handlers.
      os_assert_err (!interrupts::in_handler_mode (), EPERM);
      // Don't call this from critical regions.
      os_assert_err (!scheduler::locked (), EPERM);
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      return port::semaphore::timed_wait (this, timeout);
 
#else
 
      // Extra test before entering the loop, with its inherent weight.
      // Trade size for speed.
      {
        // ----- Enter critical section ---------------------------------------
        interrupts::critical_section ics;
 
        if (internal_try_wait_ ())
          {
            return result::ok;
          }
        // ----- Exit critical section ----------------------------------------
      }
 
      thread& crt_thread = this_thread::thread ();
 
      // Prepare a list node pointing to the current thread.
      // Do not worry for being on stack, it is temporarily linked to the
      // list and guaranteed to be removed before this function returns.
      internal::waiting_thread_node node{ crt_thread };
 
      internal::clock_timestamps_list& clock_list = clock_->steady_list ();
      clock::timestamp_t timeout_timestamp = clock_->steady_now () + timeout;
 
      // Prepare a timeout node pointing to the current thread.
      internal::timeout_thread_node timeout_node{ timeout_timestamp,
                                                  crt_thread };
 
      for (;;)
        {
          {
            // ----- Enter critical section -----------------------------------
            interrupts::critical_section ics;
 
            if (internal_try_wait_ ())
              {
                return result::ok;
              }
 
            // Add this thread to the semaphore waiting list,
            // and the clock timeout list.
            scheduler::internal_link_node (list_, node, clock_list,
                                           timeout_node);
            // state::suspended set in above link().
            // ----- Exit critical section ------------------------------------
          }
 
          port::scheduler::reschedule ();
 
          // Remove the thread from the semaphore waiting list,
          // if not already removed by post() and from the clock
          // timeout list, if not already removed by the timer.
          scheduler::internal_unlink_node (node, timeout_node);
 
          if (crt_thread.interrupted ())
            {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
#pragma GCC diagnostic push
#if defined(__clang__)
#elif defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wuseless-cast"
#endif
              trace::printf ("%s(%u) EINTR @%p %s\n", __func__,
                             static_cast<unsigned int> (timeout), this,
                             name ());
#pragma GCC diagnostic pop
#endif
              return EINTR;
            }
 
          if (clock_->steady_now () >= timeout_timestamp)
            {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
#pragma GCC diagnostic push
#if defined(__clang__)
#elif defined(__GNUC__)
#pragma GCC diagnostic ignored "-Wuseless-cast"
#endif
              trace::printf ("%s(%u) ETIMEDOUT @%p %s\n", __func__,
                             static_cast<unsigned int> (timeout), this,
                             name ());
#pragma GCC diagnostic pop
#endif
              return ETIMEDOUT;
            }
        }
 
      /* NOTREACHED */
      return ENOTRECOVERABLE;
 
#endif
    }
 
    semaphore::count_t
    semaphore::value (void) const
    {
#if !defined(OS_USE_RTOS_PORT_SEMAPHORE)
      return (count_ > 0) ? count_ : 0;
#else
      return count_;
#endif
    }
 
    result_t
    semaphore::reset (void)
    {
#if defined(OS_TRACE_RTOS_SEMAPHORE)
      trace::printf ("%s() @%p %s <%u\n", __func__, this, name (), count_);
#endif
 
      // Don't call this from interrupt handlers.
      os_assert_err (!interrupts::in_handler_mode (), EPERM);
 
#if defined(OS_USE_RTOS_PORT_SEMAPHORE)
 
      return port::semaphore::reset (this);
 
#else
 
      {
        // ----- Enter critical section ---------------------------------------
        interrupts::critical_section ics;
 
        internal_init_ ();
        return result::ok;
        // ----- Exit critical section ----------------------------------------
      }
 
#endif
    }
 
    // ------------------------------------------------------------------------
 
  } /* namespace rtos */
} /* namespace os */
 
// ----------------------------------------------------------------------------