job/semaphore: add multi-acquire

job/semaphore.hpp

@@ -32,6 +32,7 @@ namespace util::job {
         semaphore& operator= (semaphore&&) = delete;
 
         int acquire (void);
+        int acquire (int count);
         int release (void);
 
         auto   lock (void) { return acquire (); }

job/semaphore_linux.cpp

@@ -50,16 +50,18 @@ semaphore::semaphore (int initial):
 
 ///////////////////////////////////////////////////////////////////////////////
 int
-semaphore::acquire (void)
+semaphore::acquire (int count)
 {
+    CHECK_GE (count, 0);
+
     do {
         int now = m_value;
 
         // if our value is positive then attempt to decrement it and return,
         // else retry because someone interfered with us.
-        if (now > 0) {
-            if (m_value.compare_exchange_weak (now, now - 1))
-                return now - 1;
+        if (now - count >= 0) {
+            if (m_value.compare_exchange_weak (now, now - count))
+                return now - count;
             continue;
         }
 
@@ -67,16 +69,24 @@ semaphore::acquire (void)
         // there's been a modification and retry.
         if (-1 == sys_futex (&m_value, FUTEX_WAIT, now, nullptr, nullptr, 0)) {
             switch (errno) {
-            case EAGAIN: break;
-            case EINTR:  break;
-            default:
-                posix::error::throw_code ();
+                case EAGAIN: break;
+                case EINTR:  break;
+                default:
+                    posix::error::throw_code ();
             }
         }
     } while (1);
 }
 
 
+//-----------------------------------------------------------------------------
+int
+semaphore::acquire (void)
+{
+    return acquire (1);
+}
+
+
 //-----------------------------------------------------------------------------
 int
 semaphore::release (void)