/*
* Test program that illustrates how to annotate a smart pointer
* implementation. In a multithreaded program the following is relevant when
* working with smart pointers:
* - whether or not the objects pointed at are shared over threads.
* - whether or not the methods of the objects pointed at are thread-safe.
* - whether or not the smart pointer objects are shared over threads.
* - whether or not the smart pointer object itself is thread-safe.
*
* Most smart pointer implemenations are not thread-safe
* (e.g. boost::shared_ptr<>, tr1::shared_ptr<> and the smart_ptr<>
* implementation below). This means that it is not safe to modify a shared
* pointer object that is shared over threads without proper synchronization.
*
* Even for non-thread-safe smart pointers it is possible to have different
* threads access the same object via smart pointers without triggering data
* races on the smart pointer objects.
*
* A smart pointer implementation guarantees that the destructor of the object
* pointed at is invoked after the last smart pointer that points to that
* object has been destroyed or reset. Data race detection tools cannot detect
* this ordering without explicit annotation for smart pointers that track
* references without invoking synchronization operations recognized by data
* race detection tools.
*/
#include <cassert> // assert()
#include <climits> // PTHREAD_STACK_MIN
#include <iostream> // std::cerr
#include <stdlib.h> // atoi()
#ifdef _WIN32
#include <process.h> // _beginthreadex()
#include <windows.h> // CRITICAL_SECTION
#else
#include <pthread.h> // pthread_mutex_t
#endif
#include "unified_annotations.h"
static bool s_enable_annotations;
#ifdef _WIN32
class AtomicInt32
{
public:
AtomicInt32(const int value = 0) : m_value(value) { }
~AtomicInt32() { }
LONG operator++() { return InterlockedIncrement(&m_value); }
LONG operator--() { return InterlockedDecrement(&m_value); }
private:
volatile LONG m_value;
};
class Mutex
{
public:
Mutex() : m_mutex()
{ InitializeCriticalSection(&m_mutex); }
~Mutex()
{ DeleteCriticalSection(&m_mutex); }
void Lock()
{ EnterCriticalSection(&m_mutex); }
void Unlock()
{ LeaveCriticalSection(&m_mutex); }
private:
CRITICAL_SECTION m_mutex;
};
class Thread
{
public:
Thread() : m_thread(INVALID_HANDLE_VALUE) { }
~Thread() { }
void Create(void* (*pf)(void*), void* arg)
{
WrapperArgs* wrapper_arg_p = new WrapperArgs(pf, arg);
m_thread = reinterpret_cast<HANDLE>(_beginthreadex(NULL, 0, wrapper,
wrapper_arg_p, 0, NULL));
}
void Join()
{ WaitForSingleObject(m_thread, INFINITE); }
private:
struct WrapperArgs
{
WrapperArgs(void* (*pf)(void*), void* arg) : m_pf(pf), m_arg(arg) { }
void* (*m_pf)(void*);
void* m_arg;
};
static unsigned int __stdcall wrapper(void* arg)
{
WrapperArgs* wrapper_arg_p = reinterpret_cast<WrapperArgs*>(arg);
WrapperArgs wa = *wrapper_arg_p;
delete wrapper_arg_p;
return reinterpret_cast<unsigned>((wa.m_pf)(wa.m_arg));
}
HANDLE m_thread;
};
#else // _WIN32
class AtomicInt32
{
public:
AtomicInt32(const int value = 0) : m_value(value) { }
~AtomicInt32() { }
int operator++() { return __sync_add_and_fetch(&m_value, 1); }
int operator--() { return __sync_sub_and_fetch(&m_value, 1); }
private:
volatile int m_value;
};
class Mutex
{
public:
Mutex() : m_mutex()
{ pthread_mutex_init(&m_mutex, NULL); }
~Mutex()
{ pthread_mutex_destroy(&m_mutex); }
void Lock()
{ pthread_mutex_lock(&m_mutex); }
void Unlock()
{ pthread_mutex_unlock(&m_mutex); }
private:
pthread_mutex_t m_mutex;
};
class Thread
{
public:
Thread() : m_tid() { }
~Thread() { }
void Create(void* (*pf)(void*), void* arg)
{
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setstacksize(&attr, PTHREAD_STACK_MIN + 4096);
pthread_create(&m_tid, &attr, pf, arg);
pthread_attr_destroy(&attr);
}
void Join()
{ pthread_join(m_tid, NULL); }
private:
pthread_t m_tid;
};
#endif // !defined(_WIN32)
template<class T>
class smart_ptr
{
public:
typedef AtomicInt32 counter_t;
template <typename Q> friend class smart_ptr;
explicit smart_ptr()
: m_ptr(NULL), m_count_ptr(NULL)
{ }
explicit smart_ptr(T* const pT)
: m_ptr(NULL), m_count_ptr(NULL)
{
set(pT, pT ? new counter_t(0) : NULL);
}
template <typename Q>
explicit smart_ptr(Q* const q)
: m_ptr(NULL), m_count_ptr(NULL)
{
set(q, q ? new counter_t(0) : NULL);
}
~smart_ptr()
{
set(NULL, NULL);
}
smart_ptr(const smart_ptr<T>& sp)
: m_ptr(NULL), m_count_ptr(NULL)
{
set(sp.m_ptr, sp.m_count_ptr);
}
template <typename Q>
smart_ptr(const smart_ptr<Q>& sp)
: m_ptr(NULL), m_count_ptr(NULL)
{
set(sp.m_ptr, sp.m_count_ptr);
}
smart_ptr& operator=(const smart_ptr<T>& sp)
{
set(sp.m_ptr, sp.m_count_ptr);
return *this;
}
smart_ptr& operator=(T* const p)
{
set(p, p ? new counter_t(0) : NULL);
return *this;
}
template <typename Q>
smart_ptr& operator=(Q* const q)
{
set(q, q ? new counter_t(0) : NULL);
return *this;
}
T* operator->() const
{
assert(m_ptr);
return m_ptr;
}
T& operator*() const
{
assert(m_ptr);
return *m_ptr;
}
private:
void set(T* const pT, counter_t* const count_ptr)
{
if (m_ptr != pT)
{
if (m_count_ptr)
{
if (s_enable_annotations)
U_ANNOTATE_HAPPENS_BEFORE(m_count_ptr);
if (--(*m_count_ptr) == 0)
{
if (s_enable_annotations)
U_ANNOTATE_HAPPENS_AFTER(m_count_ptr);
delete m_ptr;
m_ptr = NULL;
delete m_count_ptr;
m_count_ptr = NULL;
}
}
m_ptr = pT;
m_count_ptr = count_ptr;
if (count_ptr)
++(*m_count_ptr);
}
}
T* m_ptr;
counter_t* m_count_ptr;
};
class counter
{
public:
counter()
: m_mutex(), m_count()
{ }
~counter()
{
// Data race detection tools that do not recognize the
// ANNOTATE_HAPPENS_BEFORE() / ANNOTATE_HAPPENS_AFTER() annotations in the
// smart_ptr<> implementation will report that the assignment below
// triggers a data race.
m_count = -1;
}
int get() const
{
int result;
m_mutex.Lock();
result = m_count;
m_mutex.Unlock();
return result;
}
int post_increment()
{
int result;
m_mutex.Lock();
result = m_count++;
m_mutex.Unlock();
return result;
}
private:
mutable Mutex m_mutex;
int m_count;
};
static void* thread_func(void* arg)
{
smart_ptr<counter>* pp = reinterpret_cast<smart_ptr<counter>*>(arg);
(*pp)->post_increment();
*pp = NULL;
delete pp;
return NULL;
}
int main(int argc, char** argv)
{
const int nthreads = std::max(argc > 1 ? atoi(argv[1]) : 1, 1);
const int iterations = std::max(argc > 2 ? atoi(argv[2]) : 1, 1);
s_enable_annotations = argc > 3 ? !!atoi(argv[3]) : true;
for (int j = 0; j < iterations; ++j)
{
Thread T[nthreads];
smart_ptr<counter> p(new counter);
p->post_increment();
for (int i = 0; i < nthreads; ++i)
T[i].Create(thread_func, new smart_ptr<counter>(p));
{
// Avoid that counter.m_mutex introduces a false ordering on the
// counter.m_count accesses.
const timespec delay = { 0, 100 * 1000 * 1000 };
nanosleep(&delay, 0);
}
p = NULL;
for (int i = 0; i < nthreads; ++i)
T[i].Join();
}
std::cerr << "Done.\n";
return 0;
}
// Local variables:
// c-basic-offset: 2
// End: