Add possibility to wait several times on a semaphore

include/maxscale/semaphore.hh

@@ -95,7 +95,7 @@ public:
     /**
      * @brief Waits on the semaphore.
      *
-     * If the semaphore count is greater that zero, decrements the count and
+     * If the semaphore count is greater than zero, decrements the count and
      * returns immediately. Otherwise blocks the caller until someone posts
      * the semaphore.
      *
@@ -120,6 +120,39 @@ public:
         return rc == 0;
     }
 
+    /**
+     * @brief Waits multiple times on the semaphore.
+     *
+     * If the semaphore count is greater than or equal to the specified amount,
+     * decrements the count and returns immediately. Otherwise blocks the caller
+     * until the semaphore has been posted the required number of times.
+     *
+     * @param n_wait           How many times should be waited.
+     * @param signal_approach  Whether signals should be ignored or honoured.
+     *
+     * @return How many times the semaphore has been waited on.
+     *
+     * @attention The function can return a different number than `n_wait` only
+     *            if `signal_approach` is `HONOUR_SIGNALS`.
+     */
+    size_t wait_n(size_t n_wait,
+                  signal_approach_t signal_approach = IGNORE_SIGNALS) const
+    {
+        bool waited = true;
+        size_t n_waited = 0;
+
+        while (waited && n_wait--)
+        {
+            waited = wait(signal_approach);
+            if (waited)
+            {
+                ++n_waited;
+            }
+        }
+
+        return n_waited;
+    }
+
     /**
      * @brief Waits on the semaphore.
      *
@@ -190,6 +223,46 @@ public:
         return rc == 0;
     }
 
+    /**
+     * @brief Waits on the semaphore.
+     *
+     * Waits on the sempahore the specified number of times, at most until the
+     * specified time.
+     *
+     * @param n_wait           How many times should be waited.
+     * @param ts               The *absolute* time until which the waiting at
+     *                         most is performed.
+     * @param signal_approach  Whether signals should be ignored or honoured.
+     *
+     * @return How many times the semaphore has been waited on. If the
+     *         function times out or is interrupted, then the returned
+     *         value will be less than `n_wait`.
+     *
+     * @attention If the function returns a value less than `n_count` and
+     *            `signal_approch` is `HONOUR_SIGNALS` then the caller must check
+     *            the value of `errno` to find out whether the call was timed out or
+     *            interrupted. In the former case the value will be `ETIMEDOUT`
+     *            and in the latter `EINTR.
+     */
+    size_t timedwait_n(size_t n_wait,
+                       struct timespec& ts,
+                       signal_approach_t signal_approach = IGNORE_SIGNALS) const
+    {
+        bool waited = true;
+        size_t n_waited = 0;
+
+        while (waited && n_wait--)
+        {
+            waited = timedwait(ts, signal_approach);
+            if (waited)
+            {
+                ++n_waited;
+            }
+        }
+
+        return n_waited;
+    }
+
     /**
      * @brief Waits on the semaphore.
      *
@@ -212,7 +285,43 @@ public:
      */
     bool timedwait(time_t seconds,
                    long nseconds,
-                   signal_approach_t signal_approach = IGNORE_SIGNALS) const;
+                   signal_approach_t signal_approach = IGNORE_SIGNALS) const
+    {
+        timespec ts;
+        get_current_timespec(seconds, nseconds, &ts);
+        return timedwait(ts, signal_approach);
+    }
+
+    /**
+     * @brief Waits on the semaphore.
+     *
+     * Waits on the sempahore the specified number of times at most until the
+     * specified time.
+     *
+     * @param n_wait           How many times should be waited.
+     * @param seconds          How many seconds to wait at most.
+     * @param nseconds         How many nanonseconds to wait at most.
+     * @param signal_approach  Whether signals should be ignored or honoured.
+     *
+     * @return How many times the semaphore has been waited on. If the
+     *         function times out or is interrupted, then the returned
+     *         value will be less than `n_wait`.
+     *
+     * @attention If the function returns a value less than `n_count` and
+     *            `signal_approch` is `HONOUR_SIGNALS` then the caller must check
+     *            the value of `errno` to find out whether the call was timed out or
+     *            interrupted. In the former case the value will be `ETIMEDOUT`
+     *            and in the latter `EINTR.
+     */
+    size_t timedwait_n(size_t n_wait,
+                       time_t seconds,
+                       long nseconds,
+                       signal_approach_t signal_approach = IGNORE_SIGNALS) const
+    {
+        timespec ts;
+        get_current_timespec(seconds, nseconds, &ts);
+        return timedwait_n(n_wait, ts, signal_approach);
+    }
 
     /**
      * @brief Waits on the semaphore.
@@ -237,6 +346,36 @@ public:
         return timedwait(seconds, 0, signal_approach);
     }
 
+    /**
+     * @brief Waits on the semaphore.
+     *
+     * Waits on the sempahore the specified number of times at most until the
+     * specified time.
+     *
+     * @param n_wait           How many times should be waited.
+     * @param seconds          How many seconds to wait at most.
+     * @param signal_approach  Whether signals should be ignored or honoured.
+     *
+     * @return How many times the semaphore has been waited on. If the
+     *         function times out or is interrupted, then the returned
+     *         value will be less than `n_wait`.
+     *
+     * @attention If the function returns a value less than `n_count` and
+     *            `signal_approch` is `HONOUR_SIGNALS` then the caller must check
+     *            the value of `errno` to find out whether the call was timed out or
+     *            interrupted. In the former case the value will be `ETIMEDOUT`
+     *            and in the latter `EINTR.
+     */
+    bool timedwait_n(size_t n_wait,
+                     time_t seconds,
+                     signal_approach_t signal_approach = IGNORE_SIGNALS) const
+    {
+        return timedwait_n(n_wait, seconds, 0, signal_approach);
+    }
+
+private:
+    static void get_current_timespec(time_t seconds, long nseconds, timespec* pTs);
+
 private:
     mutable sem_t m_sem;
 };

server/core/semaphore.cc

@@ -17,13 +17,14 @@
 namespace maxscale
 {
 
-bool Semaphore::timedwait(time_t seconds,
-                          long nseconds,
-                          signal_approach_t signal_approach) const
+//static
+void Semaphore::get_current_timespec(time_t seconds,
+                                     long nseconds,
+                                     timespec* pTs)
 {
     ss_dassert(nseconds <= 999999999);
 
-    timespec ts;
+    timespec& ts = *pTs;
 
     ss_debug(int rc=) clock_gettime(CLOCK_REALTIME, &ts);
     ss_dassert(rc == 0);
@@ -39,8 +40,6 @@ bool Semaphore::timedwait(time_t seconds,
     }
 
     ts.tv_nsec = nseconds_sum;
-
-    return timedwait(ts, signal_approach);
 }
 
 }

server/core/test/testsemaphore.cc

@@ -65,6 +65,14 @@ void test_simple()
     ss_dassert(rv);
     cout << "Waited" << endl;
 
+    sem2.post();
+    sem2.post();
+    sem2.post();
+
+    cout << "Waiting 3 times for semaphore with a count of 3." << endl;
+    rv = sem2.wait_n(3);
+    cout << "Waited" << endl;
+
     Semaphore sem3;
 
     time_t started;
@@ -118,10 +126,7 @@ void test_threads()
 
     cout << "Waiting for threads." << endl;
 
-    for (int i = 0; i < n_threads; ++i)
-    {
-        sem.wait();
-    }
+    sem.wait_n(n_threads);
 
     cout << "Joining threads." << endl;