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Changing a volatile application to start taking advantage of persistent memory
should rely on modifying structures and classes with only slight modifications to
functions. We will begin by modifying the queue_node structure by changing its layout as
shown in Listing 8-7.
Listing 8-7. A persistent queue implementation – modifying the queue_node struct
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#include
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#include
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#include
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#include
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#include
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struct queue_node {
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pmem::obj::p value;
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pmem::obj::persistent_ptr next;
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};
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struct queue {
...
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private:
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pmem::obj::persistent_ptr head = nullptr;
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pmem::obj::persistent_ptr tail = nullptr;
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};
As you can see, all the modifications are limited to replace the volatile pointers with
pmem:obj::persistent_ptr and to start using the p<> property.
Next, we modify a push() method, shown in Listing 8-8.
Listing 8-8. A persistent queue implementation – a persistent push() method
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void
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push(pmem::obj::pool_base &pop, int value)
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{
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pmem::obj::transaction::run(pop, [&]{
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auto node = pmem::obj::make_persistent();
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node->value = value;
Chapter 8 libpmemobj-Cpp: the adaptable language - C++ and persistent memory