dcas

memory? As discussed earlier, this is a tricky issue, because lock independence means that any thread has an unlimited opportunity to operate on any object at any time. In order to solve this problem, the previous article has made the following attempts: Use reference count for map. This policy is doomed to fail because it requires simultaneous (atomic) Update of pointers and reference counting variables (where they are in different places in memory. Although a few papers use

to B and then to a after the first read of V, and before the CAS operation was performed on V. In this scenario, the CAS operation succeeds. This kind of problem is called ABA problem. Wiki Hazard Pointer mentioned a good example of an ABA problem: in a lock free stack implementation, now to the stack, the stack of elements is [A, B, C] , point to the head top of the stack, then there is compare_and_swap(target=head, newvalue=B, expected=A) . But in this operation, the other threads A B ar

Yesterday I planned to rewrite the memory distributor. Previously, the memory distributor used in the system was inconvenient. I sacrificed simplicity to add the reference counting function and used some locks for thread safety. This time, all memory allocation and release are lockfree. Because memory blocks are single-chain tables, it is easier to implement lock free. It is difficult to use an array to manage idle resources. In this case, DCAS and si

called ABA problems. Wiki Hazard Pointer mentioned a good example of ABA problem: in a Lock free stack implementation, the elements in the stack are[A, B, C],headPoint to the top of the stack.compare_and_swap(target=head, newvalue=B, expected=A). However, in this operation, other threadsABAll are out of the stack and deletedB, AndAIn the stack, that is[A, C]. Then the previous thread'scompare_and_swapSuccessful.headPoint to a deletedB. Stackoverflow also has an example of Real-world examples f

and B, although pred it gets the and item , but at CAS the time, it may be removed by other threads. Even in the l_find process, each of its elements may be removed. The problem is that any time you get an element, you're not sure if it's still working . The validity of an element includes whether it is still in the linked list, and whether the memory it points to is still valid.Solution SolutionsThe problem of element validity determination can be solved by adding a validity flag bit to the el

the flag can be set in the lower bits, in this way, the effect of DCAS is achieved during CAS, which is equivalent to converting two logical operations into one atomic operation. Imagine the thread security of the reference counting object. The pointer encapsulated in it is thread-safe, but the object itself is not.CAS is mutually exclusive. When CAS has the same object in several threads, only one thread succeeds, and the failed thread can determine

file with the extension ". bmp"★image_cusor: The loaded bitmap is the cursor icon with the extension ". Cur"★image_icon: The loaded bitmap is an icon with the extension ". ico"▲int Load Width: The width of the bitmap load, in pixels▲int Load Height: The height of the bitmap load, in pixels▲uint Load Mode: Set the location map loading mode, if the bitmap is loaded from the file, then set to "Lr_loadfromfile"Step Two: Establish a memory DC compatible with the Windows DCWe call the Createcompatibl

device (the specified IP address must be in the O ~ Between 30, if a larger address is written. The device is still considered as 30 ). After the initialization is complete, connect nat9914 to the GUI. The initialization process 2 is shown in. The code of the control part of the process is interrupted. When nat9914 triggers an External Interrupt of the 89c51 Chip, the microcontroller terminates normal operation, pushes the field data into the stack protection, and calls the external interrupt p