From 7dfa2a34c26437c048b78f1962dc9b9cf84eb355 Mon Sep 17 00:00:00 2001
From: FritzFlorian <flo.fritz@t-online.de>
Date: Wed, 20 Mar 2019 11:14:32 +0100
Subject: [PATCH] Move thread local state OUT of thread object.

This requires the user to explicitly manage the storage duration/place of the thread local state, making a fine grained memory allocation simpler.
---
 app/test_for_new/main.cpp                  |  3 +--
 lib/pls/include/pls/internal/base/thread.h | 40 ++++++++++++++++++++++++++++------------
 test/thread_tests.cpp                      | 12 ++++++------
 3 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/app/test_for_new/main.cpp b/app/test_for_new/main.cpp
index 245c292..d04050f 100644
--- a/app/test_for_new/main.cpp
+++ b/app/test_for_new/main.cpp
@@ -8,7 +8,6 @@ int global = 0;
 
 int main() {
     // Try to use every feature, to trigger the prohibited use of new if found somewhere
-    auto t1 = create_thread([] (){}, 0);
-    t1.start();
+    auto t1 = start_thread([] (){});
     t1.join();
 }
diff --git a/lib/pls/include/pls/internal/base/thread.h b/lib/pls/include/pls/internal/base/thread.h
index c4ed39b..265190e 100644
--- a/lib/pls/include/pls/internal/base/thread.h
+++ b/lib/pls/include/pls/internal/base/thread.h
@@ -25,14 +25,28 @@ namespace pls {
                     pthread_yield();
                 }
 
+                /**
+                 * Retrieves the local state pointer.
+                 *
+                 * @tparam T The type of the state that is stored.
+                 * @return The state pointer hold for this thread.
+                 */
                 template<typename T>
                 static T* state() {
                     return reinterpret_cast<T*>(pthread_getspecific(local_storage_key_));
                 }
 
+                /**
+                 * Stores a pointer to the thread local state object.
+                 * The memory management for this has to be done by the user,
+                 * we only keep the pointer.
+                 *
+                 * @tparam T The type of the state that is stored.
+                 * @param state_pointer A pointer to the threads state object.
+                 */
                 template<typename T>
-                static void set_state(const T& state) {
-                    *reinterpret_cast<T*>(pthread_getspecific(local_storage_key_)) = state;
+                static void set_state(T* state_pointer) {
+                    pthread_setspecific(this_thread::local_storage_key_, (void*)state_pointer);
                 }
             };
 
@@ -41,26 +55,24 @@ namespace pls {
                 friend class this_thread;
                 // Keep a copy of the function (lambda) in this object to make sure it is valid when called!
                 Function function_;
-                // Keep the local state we hold in here
-                State state_;
+                State* state_pointer_;
 
                 // Keep handle to native implementation
                 pthread_t pthread_thread_;
 
                 static void* start_pthread_internal(void* thread_pointer) {
                     auto my_thread = reinterpret_cast<thread*>(thread_pointer);
-                    pthread_setspecific(this_thread::local_storage_key_, (void*)&my_thread->state_);
+                    this_thread::set_state(my_thread->state_pointer_);
                     my_thread->function_();
                     pthread_exit(nullptr);
                 }
 
             public:
-                explicit thread(const Function& function, const State& state):
-                        function_{function},
-                        state_{state},
-                        pthread_thread_{} {}
+                explicit thread(const Function& function, State* state_pointer):
+                    function_{function},
+                    state_pointer_{state_pointer},
+                    pthread_thread_{} {
 
-                void start() {
                     if (!this_thread::local_storage_key_initialized_) {
                         pthread_key_create(&this_thread::local_storage_key_, nullptr);
                         this_thread::local_storage_key_initialized_ = true;
@@ -82,10 +94,14 @@ namespace pls {
             };
 
             template<typename Function, typename State>
-            thread<Function, State> create_thread(const Function& function, const State& state) {
-                return thread<Function, State>(function, state);
+            thread<Function, State> start_thread(const Function& function, State* state_pointer) {
+                return thread<Function, State>(function, state_pointer);
             }
 
+            template<typename Function>
+            thread<Function, void> start_thread(const Function& function) {
+                return thread<Function, void>(function, nullptr);
+            }
         }
     }
 
diff --git a/test/thread_tests.cpp b/test/thread_tests.cpp
index 4ac6740..03809fe 100644
--- a/test/thread_tests.cpp
+++ b/test/thread_tests.cpp
@@ -12,18 +12,18 @@ static vector<int> local_value_two;
 
 TEST_CASE( "thread creation and joining", "[internal/base/thread.h]") {
     visited = false;
-    auto t1 = create_thread([]() { visited = true; }, 0);
-    t1.start();
+    auto t1 = start_thread([]() { visited = true; });
     t1.join();
 
     REQUIRE(visited);
 }
 
 TEST_CASE( "thread state", "[internal/base/thread.h]") {
-    auto t1 = create_thread([]() { local_value_1 = *this_thread::state<int>(); }, 1);
-    auto t2 = create_thread([]() { local_value_two = *this_thread::state<vector<int>>(); }, vector<int>{1, 2});
-    t1.start();
-    t2.start();
+    int state_one = 1;
+    vector<int> state_two{1, 2};
+    
+    auto t1 = start_thread([]() { local_value_1 = *this_thread::state<int>(); }, &state_one);
+    auto t2 = start_thread([]() { local_value_two = *this_thread::state<vector<int>>(); }, &state_two);
     t1.join();
     t2.join();
 
--
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