Add test to prohibit usage of new.

We force linker errors if the new operator is used somewhere. See NOTES.md for details.

CMakeLists.txt

@@ -28,6 +28,7 @@ add_subdirectory(lib/pls)
 
 # Include examples
 add_subdirectory(app/playground)
+add_subdirectory(app/test_for_new)
 
 # Add optional tests
 option(PACKAGE_TESTS "Build the tests" ON)

NOTES.md

+# Notes
+
+A collection of stuff that we noticed during development.
+Useful later on two write a project report and to go back
+in time to find out why certain decisions where made.
+
+## 20.03.2018 - Prohibit New
+
+We want to write this library without using any runtime memory
+allocation to better fit the needs of the embedded marked.
+To make sure we do not do so we add a trick:
+we link an new implementation into the project (when testing) that
+will cause an linker error if new is used somewhere.
+If the linker reports such an error we can switch to debugging
+by using a new implementation with a break point in it.
+
+That way we for example ruled out std::thread, as we found the dynamic
+memory allocation used in it.
+
+## 20.03.2018 - callable objects and memory allocation / why we use no std::thread
+
+When working with any sort of functionality that can be passed
+to an object or function it is usually passed as:
+1. an function pointer and a list of parameter values
+2. an lambda, capturing any surrounding parameters needed
+
+When we want to pass ANY functionality (with any number of parameters
+or captured variables) we can not determine the amount of memory before
+the call is done, making the callable (function + parameters) dynamicly
+sized.
+
+This can be a problem when implementing e.g. a thread class,
+as the callable has to be stored somewhere. The **std::thread**
+implementation allocates memory at runtime using **new** when
+called with any form of parameters for the started function.
+Because of this (and because the implementation can differ from
+system to system) we decided to not provide an **std::thread** backend
+for our internal thread class (that does not use dynamic memory,
+as it lives on the stack, knowing its size at compile time using
+templates).
+
+Lambdas can be used, as long as we are sure the outer scope still exists
+while executing (lambda lies in the callers stack), or if we copy the
+lambda manually to some memory that we know will persist during the call.
+It is important to know that the lambda wont be freed while it is
+used, as the captured variables used inside the body are held in the
+lambda object.

app/test_for_new/CMakeLists.txt

+add_executable(test_for_new main.cpp)
+
+# Example for adding the library to your app (as a cmake project dependency)
+target_link_libraries(test_for_new pls)

app/test_for_new/main.cpp

+#include <pls/internal/base/thread.h>
+#include <pls/internal/base/prohibit_new.h>
+
+using namespace pls::internal::base;
+
+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();
+    t1.join();
+}

lib/pls/CMakeLists.txt

@@ -4,7 +4,7 @@ add_library(pls STATIC
             include/pls/internal/base/choose_threading.h
             src/internal/base/spin_lock.cpp include/pls/internal/base/spin_lock.h
             src/internal/base/thread.cpp include/pls/internal/base/thread.h
-        )
+            include/pls/internal/base/prohibit_new.h)
 
 # Settings for our project...
 # ...pthreads or C++ 11 threads

lib/pls/include/pls/internal/base/prohibit_new.h

+// Prevents the use of the new operator by forcing a linker error if it is used.
+// Simply include this in your application and the linker will tell you if you
+// use new somewhere (even in third party code linked to your application).
+
+#ifndef PLS_PROHIBIT_NEW_H
+#define PLS_PROHIBIT_NEW_H
+
+#include <iostream>
+
+// Comment this out and set a debug point in the std::cout
+// line to find out where the new is located in case you
+// get an linker error.
+//#define NEW_LINK_ERROR
+
+#ifdef NEW_LINK_ERROR
+// This will cause a linker error if new is used in the code.
+// We also exit if it is somehow still called.
+inline void * operator new (std::size_t) {
+    extern int bare_new_erroneously_called();
+    exit(bare_new_erroneously_called() | 1);
+}
+#else
+// Use this + debugging point to find out where we use a new
+inline void * operator new (std::size_t) {
+//    extern int bare_new_erroneously_called();
+    std::cout << "New called! Exiting application, no dynamic memory allocation allowed!";
+    exit(1);
+}
+#endif
+
+#endif //PLS_PROHIBIT_NEW_H

lib/pls/include/pls/internal/base/thread.h

@@ -50,7 +50,7 @@ namespace pls {
                     return reinterpret_cast<T*>(pthread_getspecific(local_storage_key_));
 #endif
 #ifdef PLS_USING_CPP_THREADS
-                    reinterpret_cast<T*>(local_storage_);
+                    return reinterpret_cast<T*>(local_storage_);
 #endif
                 }
 
@@ -111,13 +111,16 @@ namespace pls {
                 explicit thread(const Function& function, const State& state):
                 function_{function},
                 state_{state},
-                std_thread_{0} {};
+                std_thread_{} {};
+
+                static void start_internal(void* my_thread_pointer) {
+                    auto my_thread = reinterpret_cast<thread*>(my_thread_pointer);
+                    this_thread::local_storage_ = reinterpret_cast<void*>(&my_thread->state_);
+                    my_thread->function_();
+                }
 
                 void start() {
-                    std_thread_ = std::thread([=](){
-                        local_storage = reinterpret_cast<void*><&this->state_>;
-                        this->function_();
-                    });
+                    std_thread_ = std::thread(start_internal, (void*)this);
                 }
 #endif
             public: