[kernel] Add clear() method to wait_queue

Allow objects to clear out the wait_queue earlier than waiting for the
destructor by moving that functionality into wait_queue::clear().

src/kernel/objects/channel.cpp

@@ -76,6 +76,7 @@ void
 channel::close()
 {
     util::scoped_lock lock {m_close_lock};
+    m_queue.clear();
     g_kernel_buffers.return_section(m_data);
     m_closed = true;
 }

src/kernel/objects/mailbox.cpp

@@ -41,8 +41,8 @@ mailbox::close()
 
     for (auto &p : m_pending) {
         delete p.val.msg;
-        p.val.sender->wake(no_message);
     }
+    m_queue.clear();
 }
 
 void

src/kernel/wait_queue.cpp

@@ -1,14 +1,7 @@
 #include "objects/thread.h"
 #include "wait_queue.h"
 
-wait_queue::~wait_queue()
-{
-    util::scoped_lock lock {m_lock};
-    for (auto *t : m_threads) {
-        if (!t->exited()) t->wake();
-        t->handle_release();
-    }
-}
+wait_queue::~wait_queue() { clear(); }
 
 void
 wait_queue::add_thread(obj::thread *t)
@@ -23,7 +16,7 @@ wait_queue::pop_exited()
 {
     while (!m_threads.empty()) {
         obj::thread *t = m_threads.first();
-        if (!t->exited())
+        if (!t->exited() && !t->ready())
             break;
 
         m_threads.pop_front();
@@ -48,3 +41,13 @@ wait_queue::pop_next_unlocked()
         return nullptr;
     return m_threads.pop_front();
 }
+
+void
+wait_queue::clear()
+{
+    util::scoped_lock lock {m_lock};
+    for (auto *t : m_threads) {
+        if (!t->exited()) t->wake();
+        t->handle_release();
+    }
+}

src/kernel/wait_queue.h

@@ -37,6 +37,9 @@ public:
     /// Get the spinlock to lock this queue
     util::spinlock & get_lock() { return m_lock; }
 
+    /// Wake and clear out all threads.
+    void clear();
+
 private:
     /// Get rid of any exited threads that are next
     /// in the queue. Caller must hold the queue lock.