Group Class

class Tasking::Group

Group represents the basic element for composing declarative recipes describing how to execute and handle a nested tree of asynchronous tasks. More...

Header:	#include <solutions/tasking/tasktree.h>
Inherits:	Tasking::ExecutableItem

List of all members, including inherited members

Note: All functions in this class are reentrant.

Public Functions

	Group(const Tasking::GroupItems &children)
	Group(std::initializer_list<Tasking::GroupItem> children)

Detailed Description

Group is a container for other group items. It encloses child tasks into one unit, which is seen by the group's parent as a single, asynchronous task. Since Group is of the GroupItem type, it may also be a child of Group.

Insert child tasks into the group by using aliased custom task names, such as, ConcurrentCallTask<ResultType> or NetworkQueryTask:

const Group group {
    NetworkQueryTask(...),
    ConcurrentCallTask<int>(...)
};

The group's behavior may be customized by inserting the items returned by parallelLimit() or workflowPolicy() functions:

const Group group {
    parallel,
    continueOnError,
    NetworkQueryTask(...),
    NetworkQueryTask(...)
};

The group may contain nested groups:

const Group group {
    finishAllAndSuccess,
    NetworkQueryTask(...),
    Group {
        NetworkQueryTask(...),
        Group {
            parallel,
            NetworkQueryTask(...),
            NetworkQueryTask(...),
        }
        ConcurrentCallTask<QString>(...)
    }
};

The group may dynamically instantiate a custom storage structure, which may be used for inter-task data exchange:

struct MyCustomStruct { QByteArray data; };

Storage<MyCustomStruct> storage;

const auto onFirstSetup = [](NetworkQuery &task) { ... };
const auto onFirstDone = [storage](const NetworkQuery &task) {
    // storage-> gives a pointer to MyCustomStruct instance,
    // created dynamically by the running task tree.
    storage->data = task.reply()->readAll();
};
const auto onSecondSetup = [storage](ConcurrentCall<QImage> &task) {
    // storage-> gives a pointer to MyCustomStruct. Since the group is sequential,
    // the stored MyCustomStruct was already updated inside the onFirstDone handler.
    const QByteArray storedData = storage->data;
};

const Group group {
    // When the group is entered by a running task tree, it creates MyCustomStruct
    // instance dynamically. It is later accessible from all handlers via
    // the *storage or storage-> operators.
    sequential,
    storage,
    NetworkQueryTask(onFirstSetup, onFirstDone, CallDoneIf::Success),
    ConcurrentCallTask<QImage>(onSecondSetup)
};

Member Function Documentation

Group::Group(const Tasking::GroupItems &children)

Constructs a group with a given list of children.

This constructor is useful when the child items of the group are not known at compile time, but later, at runtime:

const QStringList sourceList = ...;

GroupItems groupItems { parallel };

for (const QString &source : sourceList) {
    const NetworkQueryTask task(...); // use source for setup handler
    groupItems << task;
}

const Group group(groupItems);

Group::Group(std::initializer_list<Tasking::GroupItem> children)

Constructs a group from std::initializer_list given by children.

This constructor is useful when all child items of the group are known at compile time:

const Group group {
    finishAllAndSuccess,
    NetworkQueryTask(...),
    Group {
        NetworkQueryTask(...),
        Group {
            parallel,
            NetworkQueryTask(...),
            NetworkQueryTask(...),
        }
        ConcurrentCallTask<QString>(...)
    }
};

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