From c7d351f68ad65c78f035e8608952394d6d5b586e Mon Sep 17 00:00:00 2001
From: David Sansome <davidsansome@gmail.com>
Date: Wed, 2 Jun 2010 14:22:40 +0000
Subject: [PATCH] Make it possible to wait for a background thread to start

---
 src/core/backgroundthread.cpp | 18 ++++++++++++++++++
 src/core/backgroundthread.h   | 21 ++++++++++++++++-----
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/src/core/backgroundthread.cpp b/src/core/backgroundthread.cpp
index 9c4193720..bdb2aa531 100644
--- a/src/core/backgroundthread.cpp
+++ b/src/core/backgroundthread.cpp
@@ -35,3 +35,21 @@ int BackgroundThreadBase::gettid() {
   return 0;
 #endif
 }
+
+void BackgroundThreadBase::Start(bool block) {
+  if (!block) {
+    // Just start the thread and return immediately
+    QThread::start(cpu_priority_);
+    return;
+  }
+
+  // Lock the mutex so the new thread won't try to wake us up before we start
+  // waiting.
+  QMutexLocker l(&started_wait_condition_mutex_);
+
+  // Start the thread.
+  QThread::start(cpu_priority_);
+
+  // Wait for the thread to initalise.
+  started_wait_condition_.wait(l.mutex());
+}
diff --git a/src/core/backgroundthread.h b/src/core/backgroundthread.h
index 4312578fa..3a032cfb7 100644
--- a/src/core/backgroundthread.h
+++ b/src/core/backgroundthread.h
@@ -19,6 +19,8 @@
 
 #include <QThread>
 #include <QtDebug>
+#include <QWaitCondition>
+#include <QMutexLocker>
 
 #include <boost/shared_ptr.hpp>
 
@@ -67,7 +69,7 @@ class BackgroundThreadBase : public QThread {
   void set_io_priority(IoPriority priority) { io_priority_ = priority; }
   void set_cpu_priority(QThread::Priority priority) { cpu_priority_ = priority; }
 
-  virtual void Start() { QThread::start(cpu_priority_); }
+  virtual void Start(bool block = false);
 
  signals:
   void Initialised();
@@ -85,6 +87,9 @@ class BackgroundThreadBase : public QThread {
 
   IoPriority io_priority_;
   QThread::Priority cpu_priority_;
+
+  QWaitCondition started_wait_condition_;
+  QMutex started_wait_condition_mutex_;
 };
 
 // This is the templated class that stores and returns the worker object.
@@ -161,14 +166,20 @@ BackgroundThreadImplementation<InterfaceType, DerivedType>::
 
 template <typename InterfaceType, typename DerivedType>
 void BackgroundThreadImplementation<InterfaceType, DerivedType>::run() {
-  BackgroundThreadBase::SetIOPriority();
+  this->SetIOPriority();
 
-  BackgroundThread<InterfaceType>::worker_.reset(new DerivedType);
+  this->worker_.reset(new DerivedType);
 
-  emit BackgroundThreadBase::Initialised();
+  {
+    // Tell the calling thread that we've initialised the worker.
+    QMutexLocker l(&this->started_wait_condition_mutex_);
+    this->started_wait_condition_.wakeAll();
+  }
+
+  emit this->Initialised();
   QThread::exec();
 
-  BackgroundThread<InterfaceType>::worker_.reset();
+  this->worker_.reset();
 }