4 files changed, 245 insertions, 15 deletions

diff --git a/cpp/src/qpid/sys/Serializer.cpp b/cpp/src/qpid/sys/Serializer.cpp
new file mode 100644
index 0000000000..db2b3cab6d
--- /dev/null
+++ b/cpp/src/qpid/sys/Serializer.cpp
@@ -0,0 +1,125 @@
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ * 
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ */
+
+#include "qpid/sys/Serializer.h"
+#include "qpid/log/Statement.h"
+
+#include <boost/bind.hpp>
+
+#include <assert.h>
+
+namespace qpid {
+namespace sys {
+
+Serializer::Serializer(bool allowImmediate, Task notifyDispatchFn)
+    : state(IDLE), immediate(allowImmediate), notifyDispatch(notifyDispatchFn)
+{
+    if (notifyDispatch.empty())
+        notifyDispatch = boost::bind(&Serializer::notifyWorker, this);
+}
+
+Serializer::~Serializer() {
+    {
+        Mutex::ScopedLock l(lock);
+        state = SHUTDOWN;
+        lock.notify();
+    }
+    if (worker.id() != 0)
+        worker.join();
+}
+
+void Serializer::dispatch(Task& task) {
+    Mutex::ScopedUnlock u(lock);
+    // Preconditions: lock is held, state is EXECUTING or DISPATCHING
+    assert(state != IDLE);
+    assert(state != SHUTDOWN);
+    assert(state == EXECUTING || state == DISPATCHING);
+    try {
+        task();
+    } catch (const std::exception& e) {
+        QPID_LOG(error, "Unexpected exception in Serializer::dispatch"
+                 << e.what());
+        assert(0);              // Should not happen.
+    } catch (...) {
+        QPID_LOG(error, "Unexpected exception in Serializer::dispatch.");
+        assert(0);              // Should not happen.
+    }
+}
+
+void Serializer::execute(Task task) {
+    bool needNotify = false;
+    {
+        Mutex::ScopedLock l(lock);
+        assert(state != SHUTDOWN);
+        if (immediate && state == IDLE) {
+            state = EXECUTING;
+            dispatch(task);
+            if (state != SHUTDOWN) {
+                assert(state == EXECUTING);
+                state = IDLE;
+            }
+        }
+        else 
+            queue.push_back(task);
+
+        if (!queue.empty() && state == IDLE) {
+            state = DISPATCHING;
+            needNotify = true;
+        }
+    }
+    if (needNotify)
+        notifyDispatch();       // Not my function, call outside lock.
+}
+
+void Serializer::dispatch() {
+    Mutex::ScopedLock l(lock);
+    // TODO aconway 2007-07-16: This loop could be unbounded
+    // if other threads add work while we're in dispatch(Task&).
+    // If we need to bound it we could dispatch just the elements
+    // that were enqueued when dispatch() was first called - save
+    // begin() iterator and pop only up to that.
+    while (!queue.empty() && state != SHUTDOWN) {
+        assert(state == DISPATCHING);
+        dispatch(queue.front());
+        queue.pop_front();
+    }
+    if (state != SHUTDOWN) {
+        assert(state == DISPATCHING);
+        state = IDLE;
+    }
+}
+
+void Serializer::notifyWorker() {
+    if (!worker.id())
+        worker = Thread(*this);
+    else
+        lock.notify();
+}
+
+void Serializer::run() {
+    Mutex::ScopedLock l(lock);
+    while (state != SHUTDOWN) {
+        dispatch();
+        lock.wait();
+    }
+}
+
+}} // namespace qpid::sys
diff --git a/cpp/src/qpid/sys/Serializer.h b/cpp/src/qpid/sys/Serializer.h
new file mode 100644
index 0000000000..eba8e48555
--- /dev/null
+++ b/cpp/src/qpid/sys/Serializer.h
@@ -0,0 +1,105 @@
+#ifndef SERIALIZER_H
+#define SERIALIZER_H
+
+
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ * 
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ */
+
+
+#include "qpid/sys/Runnable.h"
+#include "qpid/sys/Monitor.h"
+#include "qpid/sys/Thread.h"
+
+#include <boost/function.hpp>
+#include <boost/noncopyable.hpp>
+
+#include <deque>
+
+namespace qpid {
+namespace sys {
+
+/**
+ * Execute tasks sequentially, queuing tasks when necessary to
+ * ensure only one thread at a time executes a task and tasks
+ * are executed in order.
+ */
+class Serializer : private boost::noncopyable, private Runnable
+{
+  public:
+    typedef boost::function<void()> Task;
+
+    /** Start a serializer.
+     *
+     * @param notifyDispatch Called when work is pending and there is no
+     * active dispatch thread. Must arrange for dispatch() to be called
+     * in some thread other than the calling thread and return. 
+     * By default the Serializer supplies its own dispatch thread.
+     *
+     * @param immediate Allow execute() to execute a task immediatly
+     * in the current thread.
+     */
+    Serializer(bool immediate=true, Task notifyDispatch=Task());
+
+    ~Serializer();
+    
+    /** 
+     * Task may be executed immediately in the calling thread if there
+     * are no other tasks pending or executing and the "immediate"
+     * paramater to the constructor was true. Otherwise task will be
+     * enqueued for execution by a dispatch thread.
+     */
+    void execute(Task task);
+
+    /** Execute pending tasks sequentially in calling thread.
+     * Drains the task queue and returns, does not block for more tasks.
+     * 
+     * @exception ShutdownException if the serializer is being destroyed.
+     */
+    void dispatch();
+
+  private:
+    enum State {
+        IDLE, ///< No threads are active.
+        EXECUTING, ///< execute() is executing a single task.
+        DISPATCHING, ///< dispatch() is draining the queue.
+        SHUTDOWN ///< Serializer is being destroyed.
+    };
+
+    void dispatch(Task&);
+    void notifyWorker();
+    void run();
+
+    Monitor lock;
+
+    State state;
+    bool immediate;
+    std::deque<Task> queue;
+    Thread worker;
+    Task notifyDispatch;
+};
+
+}} // namespace qpid::sys
+
+
+
+
+
+#endif  /*!SERIALIZER_H*/
diff --git a/cpp/src/qpid/sys/apr/Mutex.h b/cpp/src/qpid/sys/apr/Mutex.h
index 6679adeebb..51089c98ff 100644
--- a/cpp/src/qpid/sys/apr/Mutex.h
+++ b/cpp/src/qpid/sys/apr/Mutex.h
@@ -42,7 +42,7 @@ class Mutex : private boost::noncopyable {
     inline ~Mutex();
     inline void lock();
     inline void unlock();
-    inline void trylock();
+    inline bool trylock();
 
   protected:
     apr_thread_mutex_t* mutex;
@@ -64,8 +64,8 @@ void Mutex::unlock() {
     CHECK_APR_SUCCESS(apr_thread_mutex_unlock(mutex));
 }
 
-void Mutex::trylock() {
-    CHECK_APR_SUCCESS(apr_thread_mutex_trylock(mutex));
+bool Mutex::trylock() {
+    return apr_thread_mutex_trylock(mutex) == 0;
 }
 
 
@@ -84,8 +84,8 @@ public:
     inline void wlock();  // will write-lock
     inline void rlock();  // will read-lock
     inline void unlock();
-    inline void trywlock();  // will write-try
-    inline void tryrlock();  // will read-try
+    inline bool trywlock();  // will write-try
+    inline bool tryrlock();  // will read-try
 
   protected:
     apr_thread_mutex_t* mutex;
@@ -111,12 +111,12 @@ void RWlock::unlock() {
     CHECK_APR_SUCCESS(apr_thread_mutex_unlock(mutex));
 }
 
-void RWlock::trywlock() {
-    CHECK_APR_SUCCESS(apr_thread_mutex_trylock(mutex));
+bool RWlock::trywlock() {
+    return apr_thread_mutex_trylock(mutex) == 0;
 }
 
-void RWlock::tryrlock() {
-    CHECK_APR_SUCCESS(apr_thread_mutex_trylock(mutex));
+bool RWlock::tryrlock() {
+    return apr_thread_mutex_trylock(mutex) == 0;
 }
 
 
diff --git a/cpp/src/qpid/sys/posix/Mutex.h b/cpp/src/qpid/sys/posix/Mutex.h
index b29219235d..4cf0c3a3b0 100644
--- a/cpp/src/qpid/sys/posix/Mutex.h
+++ b/cpp/src/qpid/sys/posix/Mutex.h
@@ -43,7 +43,7 @@ public:
     inline ~Mutex();
     inline void lock();  
     inline void unlock();
-    inline void trylock();  
+    inline bool trylock();  
 
 
 protected:
@@ -127,7 +127,7 @@ struct PODMutex
 
     inline void lock();  
     inline void unlock();
-    inline void trylock();  
+    inline bool trylock();  
 
     // Must be public to be a POD:
     pthread_mutex_t mutex;
@@ -143,8 +143,8 @@ void PODMutex::unlock() {
     QPID_POSIX_THROW_IF(pthread_mutex_unlock(&mutex));
 }
 
-void PODMutex::trylock() {
-    QPID_POSIX_THROW_IF(pthread_mutex_trylock(&mutex));
+bool PODMutex::trylock() {
+    return pthread_mutex_trylock(&mutex) == 0;
 }
 
 Mutex::Mutex() {
@@ -163,8 +163,8 @@ void Mutex::unlock() {
     QPID_POSIX_THROW_IF(pthread_mutex_unlock(&mutex));
 }
 
-void Mutex::trylock() {
-    QPID_POSIX_THROW_IF(pthread_mutex_trylock(&mutex));
+bool Mutex::trylock() {
+    return pthread_mutex_trylock(&mutex) == 0;
 }