Add joinable option to SimpleThread::Options as was just done for Thread.

base/threading/simple_thread.h

Index: base/threading/simple_thread.h
diff --git a/base/threading/simple_thread.h b/base/threading/simple_thread.h
index 3deeb1018cb573c3f5e48d2b17b7c16a428aa476..f4a7b67e760a64cd1b5e417670a661c82d885046 100644
--- a/base/threading/simple_thread.h
+++ b/base/threading/simple_thread.h
@@ -46,8 +46,11 @@
 #include <string>
 #include <vector>
 
+#include "base/atomic_ref_count.h"
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
+#include "base/logging.h"
+#include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
@@ -58,25 +61,27 @@ namespace base {
 // virtual Run method, or you can use the DelegateSimpleThread interface.
 class BASE_EXPORT SimpleThread : public PlatformThread::Delegate {
  public:
-  class BASE_EXPORT Options {
+  struct BASE_EXPORT Options {
    public:
-    Options() : stack_size_(0), priority_(ThreadPriority::NORMAL) {}
-    explicit Options(ThreadPriority priority)
-        : stack_size_(0), priority_(priority) {}
-    ~Options() {}
+    Options() = default;
+    explicit Options(ThreadPriority priority_in) : priority(priority_in) {}
+    ~Options() = default;
 
-    // We use the standard compiler-supplied copy constructor.
+    // Allow copies.
+    Options(const Options& other) = default;
+    Options& operator=(const Options& other) = default;
 
     // A custom stack size, or 0 for the system default.
-    void set_stack_size(size_t size) { stack_size_ = size; }
-    size_t stack_size() const { return stack_size_; }
+    size_t stack_size = 0;
 
-    // A custom thread priority.
-    void set_priority(ThreadPriority priority) { priority_ = priority; }
-    ThreadPriority priority() const { return priority_; }
-   private:
-    size_t stack_size_;
-    ThreadPriority priority_;
+    ThreadPriority priority = ThreadPriority::NORMAL;
+
+    // If false, the underlying thread's PlatformThreadHandle will not be kept
+    // around and as such the SimpleThread instance will not be Join()able and
+    // must not be deleted before Run() is invoked. After that, it's up to
+    // the subclass to determine when it is safe to delete itself, see
+    // DelegateSimpleThread for a safe option.
+    bool joinable = true;
   };
 
   // Create a SimpleThread.  |options| should be used to manage any specific
@@ -106,7 +111,7 @@ class BASE_EXPORT SimpleThread : public PlatformThread::Delegate {
   // Return True if Start() has ever been called.
   bool HasBeenStarted();
 
-  // Return True if Join() has evern been called.
+  // Return True if Join() has ever been called.
   bool HasBeenJoined() { return joined_; }
 
   // Overridden from PlatformThread::Delegate:
@@ -116,19 +121,44 @@ class BASE_EXPORT SimpleThread : public PlatformThread::Delegate {
   const std::string name_prefix_;
   std::string name_;
   const Options options_;
-  PlatformThreadHandle thread_;  // PlatformThread handle, invalid after Join!
+  PlatformThreadHandle thread_;  // PlatformThread handle, reset after Join.
   WaitableEvent event_;          // Signaled if Start() was ever called.
-  PlatformThreadId tid_;         // The backing thread's id.
-  bool joined_;                  // True if Join has been called.
+  PlatformThreadId tid_ = kInvalidThreadId;  // The backing thread's id.
+  bool joined_ = false;                      // True if Join has been called.
+
+  DISALLOW_COPY_AND_ASSIGN(SimpleThread);
 };
 
+// A SimpleThread which delegates Run() to its Delegate. The registered Delegate
+// must outlive its Run() invocation(s). As such, non-joinable
+// DelegateSimpleThread are safe to delete after Start() so long as the
+// Delegate's lifetime respects the aforementioned condition.
 class BASE_EXPORT DelegateSimpleThread : public SimpleThread {
  public:
   class BASE_EXPORT Delegate {
    public:
-    Delegate() { }
-    virtual ~Delegate() { }
+    Delegate();
+    virtual ~Delegate();
+
+    // Invokes Run() and manages |active_runners_|.
+    void RunHelper();
+
+   private:
+    // Run() is private pure virtual because only RunHelper() should invoke it,
+    // but it's still up to the implementer to define it.
     virtual void Run() = 0;
+
+#if DCHECK_IS_ON()
+    // Maintains a count of active Run() calls -- there can be more than one
+    // when Delegate is used in a DelegateSimpleThreadPool.
+    AtomicRefCount active_runners_ = 0;
+
+    // Signaled when |active_runners_| is decremented, auto-reset after the
+    // signal is observed.
+    WaitableEvent active_runners_decremented_;
+#endif  // DCHECK_IS_ON()
+
+    DISALLOW_COPY_AND_ASSIGN(Delegate);
   };
 
   DelegateSimpleThread(Delegate* delegate,
@@ -142,6 +172,12 @@ class BASE_EXPORT DelegateSimpleThread : public SimpleThread {
 
  private:
   Delegate* delegate_;
+
+#if DCHECK_IS_ON()
+  bool ran_ = false;
+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(DelegateSimpleThread);
 };
 
 // DelegateSimpleThreadPool allows you to start up a fixed number of threads,
@@ -186,6 +222,8 @@ class BASE_EXPORT DelegateSimpleThreadPool
   std::queue<Delegate*> delegates_;
   base::Lock lock_;            // Locks delegates_
   WaitableEvent dry_;    // Not signaled when there is no work to do.
+
+  DISALLOW_COPY_AND_ASSIGN(DelegateSimpleThreadPool);
 };
 
 }  // namespace base