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Boris Smidt 2016-04-24 14:50:50 +02:00 committed by Thibault Kruse
parent e8dea3807a
commit 757737e86d
1 changed files with 35 additions and 35 deletions
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CppCoreGuidelines.md
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@ -10786,13 +10786,13 @@ A `thread` that has not been `detach()`ed when it is destroyed terminates the pr
void f() { std::cout << "Hello "; }
struct F {
void operator()() { std::cout << "parallel world "; }
void operator()() { std::cout << "parallel world "; }
};
int main()
{
std::thread t1{f}; // f() executes in separate thread
std::thread t2{F()}; // F()() executes in separate thread
std::thread t1{f}; // f() executes in separate thread
std::thread t2{F()}; // F()() executes in separate thread
} // spot the bugs
##### Example
@ -10800,13 +10800,13 @@ A `thread` that has not been `detach()`ed when it is destroyed terminates the pr
void f() { std::cout << "Hello "; }
struct F {
void operator()() { std::cout << "parallel world "; }
void operator()() { std::cout << "parallel world "; }
};
int main()
{
std::thread t1{f}; // f() executes in separate thread
std::thread t2{F()}; // F()() executes in separate thread
std::thread t1{f}; // f() executes in separate thread
std::thread t2{F()}; // F()() executes in separate thread
t1.join();
t2.join();
@ -10992,20 +10992,20 @@ A `wait` without a condition can miss a wakeup or wake up simply to find that th
void thread1()
{
while (true) {
// do some work ...
std::unique_lock<std::mutex> lock(mx);
cv.notify_one(); // wake other thread
}
while (true) {
// do some work ...
std::unique_lock<std::mutex> lock(mx);
cv.notify_one(); // wake other thread
}
}
void thread2()
{
while (true) {
std::unique_lock<std::mutex> lock(mx);
cv.wait(lock); // might block forever
// do work ...
}
while (true) {
std::unique_lock<std::mutex> lock(mx);
cv.wait(lock); // might block forever
// do work ...
}
}
Here, if some other `thread` consumes `thread1`'s notification, `thread2` can wait forever.
@ -11015,30 +11015,30 @@ Here, if some other `thread` consumes `thread1`'s notification, `thread2` can wa
template<typename T>
class Sync_queue {
public:
void put(const T& val);
void put(T&& val);
void get(T& val);
void put(const T& val);
void put(T&& val);
void get(T& val);
private:
mutex mtx;
condition_variable cond; // this controls access
list<T> q;
mutex mtx;
condition_variable cond; // this controls access
list<T> q;
};
template<typename T>
void Sync_queue<T>::put(const T& val)
{
lock_guard<mutex> lck(mtx);
q.push_back(val);
cond.notify_one();
lock_guard<mutex> lck(mtx);
q.push_back(val);
cond.notify_one();
}
template<typename T>
void Sync_queue<T>::get(T& val)
{
unique_lock<mutex> lck(mtx);
cond.wait(lck,[this]{ return !q.empty(); }); // prevent spurious wakeup
val=q.front();
q.pop_front();
unique_lock<mutex> lck(mtx);
cond.wait(lck,[this]{ return !q.empty(); }); // prevent spurious wakeup
val=q.front();
q.pop_front();
}
Now if the queue is empty when a thread executing `get()` wakes up (e.g., because another thread has gotton to `get()` before it),
@ -11251,15 +11251,15 @@ It's error-prone and requires expert level knowledge of language features, machi
##### Example, bad
extern atomic<Link*> head; // the shared head of a linked list
extern atomic<Link*> head; // the shared head of a linked list
Link* nh = new Link(data,nullptr); // make a link ready for insertion
Link* h = head.load(); // read the shared head of the list
Link* nh = new Link(data,nullptr); // make a link ready for insertion
Link* h = head.load(); // read the shared head of the list
do {
if (h->data<=data) break; // if so, insert elsewhere
nh->next = h; // next element is the previous head
} while (!head.compare_exchange_weak(h,nh)); // write nh to head or to h
if (h->data<=data) break; // if so, insert elsewhere
nh->next = h; // next element is the previous head
} while (!head.compare_exchange_weak(h,nh)); // write nh to head or to h
Spot the bug.
It would be really hard to find through testing.