[英]pthread_create in constructor segfault
I discovered, in this little example below, if I call pthread_create in the constructor of my struct, I get a segfault randomly on the call to pthread_mutex_lock().我发现,在下面的这个小例子中,如果我在我的结构的构造函数中调用 pthread_create,我会在调用 pthread_mutex_lock() 时随机得到一个段错误。
And sometimes the name field is empty for the first philosopher.有时,第一位哲学家的姓名字段为空。
If I move pthread_create to a run() function after the constructor, no segfault.如果我在构造函数之后将 pthread_create 移动到 run() function,则没有段错误。
It seems the call to pthread_create happens before all the members are initialized.似乎对 pthread_create 的调用发生在所有成员初始化之前。 Shouldn't the member init list of the class be completed before the call to constructor body? class 的成员初始化列表不应该在调用构造函数体之前完成吗?
Thanks for any tips!感谢您的任何提示!
clang version 9.0.0 (tags/RELEASE_900/final) Target: x86_64-apple-darwin17.7.0 clang 版本 9.0.0 (tags/RELEASE_900/final) 目标:x86_64-apple-darwin17.7.0
Sincerely, George真诚的,乔治
#include <array>
#include <iostream>
#include <pthread.h>
#include <string>
#include <vector>
using namespace std;
struct chopstick
{
pthread_mutex_t mutex;
chopstick()
{
pthread_mutex_init(&mutex,nullptr);
}
~chopstick()
{
pthread_mutex_destroy(&mutex);
}
};
void* feed(void* data);
struct philosopher
{
pthread_t thread;
string name;
unsigned mouthfuls;
chrono::seconds sec;
chopstick &left, &right;
pthread_t& get_thread() { return thread; }
philosopher(const string &s, chopstick &l, chopstick &r): name(move(s)), left(l), right(r), mouthfuls(0)
/*
enable below to avoid segfault
{}
void run()
*/
{
pthread_create(&thread, nullptr, feed, this);
};
};
void* feed(void* data)
{
philosopher & a = *static_cast<philosopher*>(data);
while (a.mouthfuls < 20)
{
pthread_mutex_lock(&a.left.mutex);
pthread_mutex_lock(&a.right.mutex);
cout << "Apostle " << a.name << " thread id " << pthread_self()
<< " acquired a chopstick at count: " << a.mouthfuls << endl;
++a.mouthfuls;
pthread_mutex_unlock(&a.right.mutex);
pthread_mutex_unlock(&a.left.mutex);
}
return nullptr;
}
int main (int argc, char const * argv[])
{
array<string, 12> names {"John", "Thaddeus", "Simon Peter", "James", "Judhas", "Bartholomew", "Matthew", "Philip", "Simon Zealot", "Thomas", "Andrew", "James the Lesser" };
array<chopstick,names.size()> sticks;
vector<philosopher> philosophers;
for (int i=0; i+1<names.size(); ++i)
philosophers.emplace_back( names[i],sticks[i],sticks[i+1] );
philosophers.emplace_back(names[names.size()-1], sticks[0],sticks[names.size()-1]);
//for (philosopher& a: philosophers) a.run(); //<-- enable to avoid segfault
for (philosopher& a: philosophers) pthread_join(a.get_thread(), nullptr);
return 0;
}
std::vector
resizes when the code does philosophers.emplace_back()
, which can move the elements in memory, so that their previous addresses become invalid and the feed()
function ends up accessing objects using their old invalid addresses. std::vector
在代码执行philosophers.emplace_back()
时调整大小,这可以移动 memory 中的元素,从而使它们以前的地址变得无效,并且feed()
function 最终使用其旧的无效地址访问对象。
A fix would be to make the philosopher
class non-copyable and non-movable, and then use std::list<philosopher>
or std::forward_list<philosopher>
instead of std::vector<philosopher>
.解决方法是使philosopher
class 不可复制和不可移动,然后使用std::list<philosopher>
或std::forward_list<philosopher>
代替std::vector<philosopher>
。 std::list
and std::forward_list
do not move elements in memory and hence are capable of storing non-copyable and non-moveable objects. std::list
和std::forward_list
不会移动 memory 中的元素,因此能够存储不可复制和不可移动的对象。
You may also like to use std::thread
instead of pthread_t
, and std::mutex
instead of pthread_mutex_t
.您可能还想使用std::thread
代替pthread_t
和std::mutex
代替pthread_mutex_t
。 The std
classes are non-copyable/movable which would prevent you from making this error at compile-time. std
类是不可复制/可移动的,这将防止您在编译时出现此错误。 Also, the code doesn't check return values of the pthread functions for errors, whereas std::thread
and std::mutex
do that for you.此外,代码不会检查 pthread 函数的返回值是否有错误,而std::thread
和std::mutex
会为您执行此操作。
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