Report a bug of Engine::Get() #12613
Description
GraphExecutor should hold Engine::_GetSharedRef() to a class member engine_ref_, or sometimes Engine might be deconstructed before GraphExecutor was deconstructed. Note that in ~GraphExecutor(), Engine::Get()->DeleteOperator() was called.
This bug is similar to #309 , which has been fixed yet. In this bug, sometimes ObjectPool<ThreadedOpr>, ObjectPool<OprBlock>, ObjectPool<VersionedVarBlock>, common::ObjectPool<ThreadedVar>, might be deconstructed before ThreadedEngine was deconstructed.
Why this shared_ptr bug appears everywhere? It's a general C++ problem. A simple example as follow:
engine.h
#pragma once
#include <memory>
class Eng {
public:
virtual ~Eng() = default;
virtual void Print() const = 0;
};
// src/engine/engine.cc
class Engine : public Eng {
public:
Engine();
~Engine();
static std::shared_ptr<Engine> _GetSharedRef();
static Engine* Get();
void Print() const;
private:
char *name_ = nullptr;
};
typedef Eng *get_t();
typedef std::shared_ptr<Engine> get_ref_t();
engine.cc
#include "engine.h"
#include <stdio.h>
Engine::Engine() {
name_ = new char[8];
snprintf(name_, 8, "HELLO");
}
Engine::~Engine() {
printf("BEGIN ~Engine\n");
if (name_) delete name_;
printf(" END ~Engine\n");
}
std::shared_ptr<Engine> Engine::_GetSharedRef() {
static std::shared_ptr<Engine> sptr(new Engine());
return sptr;
}
Engine* Engine::Get() {
static Engine *inst = _GetSharedRef().get(); // Dangerous!
return inst;
}
void Engine::Print() const {
printf("name=%s\n", name_);
}
extern "C" Eng *get() {
return Engine::Get();
}
extern "C" std::shared_ptr<Engine> get_ref() {
return Engine::_GetSharedRef();
}
executor.h
#pragma once
#include <memory>
#include "engine.h"
class Executor {
public:
virtual ~Executor() = default;
virtual void Print() = 0;
};
// src/executor/graph_executor.cc
class GraphExecutor : public Executor {
public:
GraphExecutor(void *eng);
~GraphExecutor();
static std::shared_ptr<GraphExecutor> _GetSharedRef(void *eng);
static GraphExecutor* Get(void *eng);
void Print();
private:
void *eng_;
std::shared_ptr<Engine> engine_ref_; // TODO: important!
};
typedef Executor *create_t(void *);
executor.cc
#include "executor.h"
#include <dlfcn.h>
#include <stdio.h>
#include "engine.h"
GraphExecutor::GraphExecutor(void *eng) {
eng_ = eng;
get_ref_t *get_ref = (get_ref_t *) dlsym(eng_, "get_ref");
engine_ref_ = get_ref(); // TODO: important!
}
GraphExecutor::~GraphExecutor() {
printf("BEGIN ~GraphExecutor\n");
Print();
printf(" END ~GraphExecutor\n");
}
void GraphExecutor::Print() {
get_t *get = (get_t *) dlsym(eng_, "get");
Eng *eng = get();
eng->Print();
}
std::shared_ptr<GraphExecutor> GraphExecutor::_GetSharedRef(void *eng) {
static std::shared_ptr<GraphExecutor> sptr(new GraphExecutor(eng));
return sptr;
}
GraphExecutor* GraphExecutor::Get(void *eng) {
static GraphExecutor *inst = _GetSharedRef(eng).get(); // Dangerous!
return inst;
}
extern "C" Executor *create(void *eng) {
return GraphExecutor::Get(eng);
}
test.cc
#include "engine.h"
#include "executor.h"
#include <dlfcn.h>
#include <stdio.h>
int main() {
void *handle_engine = dlopen("libengine.so", RTLD_LAZY);
void *handle = dlopen("libexe.so", RTLD_LAZY);
create_t *create = (create_t *) dlsym(handle, "create");
Executor *executor = create(handle_engine);
executor->Print();
//dlclose(handle_engine);
//dlclose(handle);
return 0;
}
Makefile
all:
gcc -std=c++11 -g engine.cc -fPIC -shared -o libengine.so
gcc -std=c++11 -g executor.cc -fPIC -shared -o libexe.so
g++ -std=c++11 -g test.cc -rdynamic -ldl -o b.out
make
./b.out
You will run well. But if there is no "engine_ref_ = get_ref();" in GraphExecutor::GraphExecutor(void *eng), it will coredump. This is the same problem as the bug.