C++ Guidelines for Multithreaded System

-
Mutithreading è Parallelism è Achieve concurrency.
Below are some of the guidelines to follow for building C++ Multithreaded system.

Ø std::thread function arguments are pass by value by default.
Thread function arguments are pass by value by default. So, if you want the change to be persisted in the arguments passed in , then pass them by reference using std::ref().

Ø Protect shared data or resource using critical section.
    In a multithreaded environment if there are more than one thread sharing the resource/data then often it results in a undefined behaviour if the resource/shared data is not protected using synchronise mechanism. So, the shared resource/data must be protected with std::mutex .

Ø Release lock after critical section.
If a thread T1 acquires lock (mutex.lock()) before entering critical section and forgets to unlock(mutex.unlock()) then all the other threads will be blocked indefinitely and the program might hang because thread T1 gets hold of mutex and all the other threads are essentially waiting to acquire the lock. So, either use std::lock_guard() or std::unique_lock<std::mutex> lock() which used RAII to manage the creating and destruction object once it goes out of scope.

Ø Critical section must have only atomic operations.
When one thread is inside critical section then all other threads trying to enter the critical section are essentially blocked. So, the operations inside critical section must be atomic or as compact and small as possible.

Ø Acquire multiple locks in the same order to avoid deadlock

Ø Don’t try to acquire std::mutex lock twice

Ø Use join() to wait for background threads before terminating an application
    The program might crash if you forget to join a thread or detach before the main program terminates.
    The program will crash because at the end of the main function, when  thread T1 goes out of scope and the thread destructor is called. Inside the destructor, a check is performed to see if thread T1 is joinable. A joinable thread is a thread that has not been detached. If the thread is joinable it calls std::terminate.

Ø std::thread::join() blocks the calling thread

Comments

Post a Comment

Popular posts from this blog

Signalling System #7(SS7) Protocol.

-
Image
            Signaling System No. 7 ( SS7 ) is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls. Other uses include number translation, prepaid billing mechanisms, short message service (SMS), and a variety of other mass market services. SS5 and earlier systems used in-band signaling(In telecommunications, In-band signaling is the sending of metadata and control information in the same band, on the same channel, as used for data.). SS6 and SS7 implement out-of-band (out-of-band control signaling, signaling bits are sent in special order in a dedicated signaling frame.) signaling protocols.         The term signaling , when used in telephony, refers to the exchange of control information associated with the establishment of a telephone call on a telecommunications circuit. An example of this control information is the digits dialed by t
Read more

std::shared_ptr

-
Image
std::shared_ptr  for shared ownership An object accessed via std::shared_ptr s has its lifetime managed by those pointers through shared ownership. No specific std::shared_ptr owns the object. Instead all shared_ptr’s pointing to it collaborates to ensure its destruction at the point where it’s no longer needed. When the last shared_ptr pointing to an object stops pointing there, that shared_ptr destroys the object it points to. A shared_ptr can tell whether it’s the last one pointing to a resource by consulting the resource’s reference count, a value associated with the resource that keeps track of how many shared_ptrs point to it. Shared_ptrs constructors increments this count shared_ptr s destructors decrements it and copy assignment operators do both. If sp1 and sp2 are shared_ptr s to different objects, the assignment “ sp1=sp2 ” , modifies sp1 such that it points  to the object pointed to by sp2 . sp1 reference count is decremented, while that for the object point
Read more