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C++0x atomic implementation in c++98 question about __sync_synchronize()


C++0x atomic implementation in c++98 question about __sync_synchronize()

By : Karthick Govindaraj
Date : October 28 2020, 04:55 PM
With these it helps I have written the followin atomic template with a view to mimicing the atomic operations which will be available in the upcoming c++0x standard. , First, some petty remarks:
code :


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What does __sync_synchronize do?

What does __sync_synchronize do?


By : Jimi Dickinson
Date : March 29 2020, 07:55 AM
it should still fix some issue It is a atomic builtin for full memory barrier.
Qt atomic operations implementation

Qt atomic operations implementation


By : user2455385
Date : March 29 2020, 07:55 AM
it helps some times Atomic operations cannot be achieved in plain C++ so they are implemented directly in assembly for each specific processor architecture.
Here is the source for Qt's atomic operations for x86 processors: http://qt.gitorious.org/qt/qt/blobs/4.7/src/corelib/arch/i386/qatomic_i386.s
atomic question from core java

atomic question from core java


By : user3097134
Date : March 29 2020, 07:55 AM
Hope that helps The flipDone method is executed by the computer in three distinct steps:
code :
Read the value of memory location labeled done into ALU
Flip the value (i.e true -> false or false -> true)
Write the new value into the memory location done
Thread 1                             Thread 2
-----------------------------------------------------------------------
Read value of done, false
Invert that value to true
Write the new value, true, to done       
                                     Read value of done, now true
                                     Invert that value to false
                                     Write the new value, false, to done
Thread 1                             Thread 2
-----------------------------------------------------------------------
Read value of done, false
Invert that value to true            Read value of done, false
Write the new value, true, to done   Invert that value to true    
                                     Write the new value, true, to done
C++11 Implementation of Spinlock using <atomic>

C++11 Implementation of Spinlock using <atomic>


By : Fionna Cervano
Date : March 29 2020, 07:55 AM
Any of those help The problem is that compare_exchange_weak updates the unlatched variable once it fails. From the documentation of compare_exchange_weak:
code :
while(!latch.compare_exchange_weak(unlatched, true, std::memory_order_acquire)) {
    unlatched = false;
}
C++: __sync_synchronize() still needed with std::atomic?

C++: __sync_synchronize() still needed with std::atomic?


By : Hannah Li
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further Whilst it is impossible to say from your simplified code what actually goes on in your actual application, the fact that __sync_synchronize helps, and the fact that this function is a memory barrier tells me that you are writing things in the one thread that the other thread is reading, in a way that isn't atomic.
An example:
code :
thread_1:

    object *p = new object;
    p->x = 1;
    b.exchange(p);   /* give pointer p to other thread */

thread_2:

    object *p = b.load();
    if (p->x == 1) do_stuff();
    else error("Huh?");
  std::atomic<bool> flag(false);
  value = 42;
  flag.store(true);

  ....
  while(!flag.load());
  print(value); 
  flag.store(true);
  value = 42;
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