LibThread: Improve semantics of Thread::join, and remove Thread::quit.

Thread::quit was created before the pthread_create_helper in pthread.cpp
that automagically calls pthread_exit from all pthreads after the user's
thread function exits. It is unused, and unecessary now.

Cleanup some logging, and make join return a Result<T, ThreadError>.
This also adds a new type, LibThread::ThreadError as an
AK::DistinctNumeric. Hopefully, this will make it possible to have a
Result<int, ThreadError> and have it compile? It also makes it clear
that the int there is an error at the call site.

By default, the T on join is void, meaning the caller doesn't care about
the return value from the thread.

As Result is a [[nodiscard]] type, also change the current caller of
join to explicitly ignore it.

Move the logging out of join as well, as it's the user's
responsibility whether to log or not.

1 files changed, 25 insertions, 2 deletions

diff --git a/Libraries/LibThread/Thread.h b/Libraries/LibThread/Thread.h
index 28fba0d78a..7fff078827 100644
--- a/Libraries/LibThread/Thread.h
+++ b/Libraries/LibThread/Thread.h
@@ -26,13 +26,17 @@
 
 #pragma once
 
+#include <AK/DistinctNumeric.h>
 #include <AK/Function.h>
+#include <AK/Result.h>
 #include <AK/String.h>
 #include <LibCore/Object.h>
 #include <pthread.h>
 
 namespace LibThread {
 
+TYPEDEF_DISTINCT_ORDERED_ID(int, ThreadError);
+
 class Thread final : public Core::Object {
     C_OBJECT(Thread);
 
@@ -40,8 +44,11 @@ public:
     virtual ~Thread();
 
     void start();
-    void join();
-    void quit(void* code = 0);
+
+    template<typename T = void>
+    Result<T, ThreadError> join();
+
+    String thread_name() const { return m_thread_name; }
     pthread_t tid() const { return m_tid; }
 
 private:
@@ -51,4 +58,20 @@ private:
     String m_thread_name;
 };
 
+template<typename T>
+Result<T, ThreadError> Thread::join()
+{
+    void* thread_return = nullptr;
+    int rc = pthread_join(m_tid, &thread_return);
+    if (rc != 0) {
+        return ThreadError { rc };
+    }
+
+    m_tid = 0;
+    if constexpr (IsVoid<T>::value)
+        return {};
+    else
+        return { static_cast<T>(thread_return) };
+}
+
 }