Make expire time atomic

It is checked in WebController::expireSessions(), possibly concurrently
with it being updated in WebSession::setState().

Made Time ctor noexcept and made copy and move trivial to meet
std::atomic requirements.

While I don't expect this to have caused any real issues
(expireSessions() would likely just read the old or the new version),
thread sanitizer doesn't like it, and it's more correct to make it
atomic.

Author: RockinRoel

src/web/TimeUtil.C

@@ -4,27 +4,31 @@
 
 namespace Wt {
 
-Time::Time()
+Time::Time() noexcept
 {
   tp_ = std::chrono::steady_clock::now();
 }
 
+#ifdef WT_TARGET_JAVA
 Time::Time(const Time &other)
 {
   tp_ = other.tp_;
 }
+#endif // WT_TARGET_JAVA
 
 Time& Time::operator+= (int msec)
 {
   tp_ += std::chrono::milliseconds(msec);
   return *this;
 }
 
+#ifdef WT_TARGET_JAVA
 Time& Time::operator= (const Time &other)
 {
   tp_ = other.tp_;
   return *this;
 }
+#endif
 
 Time Time::operator+ (int msec) const
 {

src/web/TimeUtil.h

@@ -19,19 +19,25 @@ namespace Wt {
 class WT_API Time
 {
 public:
-  Time(); // now
+  Time() noexcept; // now
+#ifdef WT_TARGET_JAVA
   Time(const Time &other);
+#endif // WT_TARGET_JAVA
 
   Time operator+ (int msec) const;
   Time& operator+= (int msec);
+
+#ifdef WT_TARGET_JAVA
   Time& operator= (const Time &other);
+#endif
 
   int operator- (const Time& other) const; // milliseconds
 
 private:
   std::chrono::steady_clock::time_point tp_;
 };
 
+
 }
 
 #endif // TIMEUTIL_H_

src/web/WebSession.h

@@ -34,6 +34,10 @@
 #include "Wt/WEnvironment.h"
 #include "Wt/WLogger.h"
 
+#ifdef WT_THREADED
+#include <atomic>
+#endif // WT_THREADED
+
 namespace Wt {
 
 class WebController;
@@ -118,7 +122,7 @@ class WT_API WebSession
   WObject *emitStackTop();
 
 #ifndef WT_TARGET_JAVA
-  const Time& expireTime() const { return expire_; }
+  Time expireTime() const { return expire_; }
 #endif // WT_TARGET_JAVA
 
   bool dead() { return state_ == State::Dead; }
@@ -315,8 +319,12 @@ class WT_API WebSession
   int deferCount_;
 
 #ifndef WT_TARGET_JAVA
+#ifdef WT_THREADED
+  std::atomic<Time> expire_;
+#else
   Time             expire_;
 #endif
+#endif
 
 #ifdef WT_BOOST_THREADS
   std::condition_variable recursiveEvent_, recursiveEventDone_;