pmem::obj::transaction::automatic Class Reference

C++ automatic scope transaction class. More...

#include <libpmemobj++/transaction.hpp>

Classes
class	uncaught_exception_counter
	Internal class for counting active exceptions. More...

Public Member Functions
template<typename... L>
	automatic (obj::pool_base &pop, L &... locks)
	RAII constructor with pmem resident locks. More...
	~automatic () noexcept(false)
	Destructor. More...
	automatic (const automatic &p)=delete
	Deleted copy constructor.
	automatic (const automatic &&p)=delete
	Deleted move constructor.
automatic &	operator= (const automatic &p)=delete
	Deleted assignment operator.
automatic &	operator= (automatic &&p)=delete
	Deleted move assignment operator.

Detailed Description

C++ automatic scope transaction class.

This class is one of pmemobj transaction handlers. All operations between creating and destroying the transaction object are treated as performed in a transaction block and can be rolled back. If you have a C++17 compliant compiler, the automatic transaction will commit and abort automatically depending on the context of object destruction.

The locks are held for the entire duration of the transaction. They are released at the end of the scope, so within the catch block, they are already unlocked. If the cleanup action requires access to data within a critical section, the locks have to be manually acquired once again.

The typical usage example would be:

#include <libpmemobj++/make_persistent.hpp>
#include <libpmemobj++/mutex.hpp>
#include <libpmemobj++/persistent_ptr.hpp>
#include <libpmemobj++/pext.hpp>
#include <libpmemobj++/pool.hpp>
#include <libpmemobj++/shared_mutex.hpp>
#include <libpmemobj++/transaction.hpp>

using namespace pmem::obj;

int
automatic_tx_example()
{
    // pool root structure
    struct root {
        mutex pmutex;
        shared_mutex shared_pmutex;
        p<int> count;
        persistent_ptr<root> another_root;
    };

    // create a pmemobj pool
    auto pop = pool<root>::create("poolfile", "layout", PMEMOBJ_MIN_POOL);
    auto proot = pop.root();

    try {
        transaction::automatic tx(pop, proot->pmutex,
                      proot->shared_pmutex);

        // atomically allocate objects
        proot->another_root = make_persistent<root>();

        // atomically modify objects
        proot->count++;

        // manual transaction commit is no longer necessary
    } catch (pmem::transaction_error &) {
        // an internal transaction error occurred, tx aborted
        // reacquire locks if necessary
    } catch (...) {
        // some other exception thrown, tx aborted
        // reacquire locks if necessary
    }

    // In complex cases with library calls, remember to check the status of
    // the previous transaction.
    return transaction::error();
}

Constructor & Destructor Documentation

automatic()

template<typename... L>

pmem::obj::transaction::automatic::automatic ( obj::pool_base &  pop, L &...  locks  )

inline

RAII constructor with pmem resident locks.

Start pmemobj transaction and add list of locks to new transaction. The list of locks may be empty.

This class is only available if the __cpp_lib_uncaught_exceptions feature macro is defined. This is a C++17 feature.

Parameters

[in,out]	pop	pool object.
[in,out]	locks	locks of obj::mutex or obj::shared_mutex type.

Exceptions

pmem::transaction_error

when pmemobj_tx_begin function or locks adding failed.

~automatic()

pmem::obj::transaction::automatic::~automatic ( )

inlinenoexcept

Destructor.

End pmemobj transaction. Depending on the context of object destruction, the transaction will automatically be either committed or aborted.

Exceptions

pmem::transaction_error

if the transaction got aborted without an active exception.

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The documentation for this class was generated from the following file:

• libpmemobj++/transaction.hpp