Scoped Value

1 minute read

https://openjdk.org/jeps/446

Immutable and better way to share data between threads

Scoped Value are only available for use within the dynamic scope of the method

Advantages

  • during the bounded period of execution of a method
  • bound during start of scope and unbounded during end of scope (even exception)
  • Rebinding allowed but cannot modify Scoped Value
  • No cleanup required. Automatically handled

Bind the Scoped Values to the Object

all methods return boolean boolean result = ScopedValue.callWhere(studentScopedValue, hp, CallableClass::methodName);

//bind a key (studentScopedValue) to a value (hp) with an operation op (handleUser())
ScopedValue.callWhere(studentScopedValue, hp, CallableClass::methodName);//using a callable

//binds studentScopedValue with harryPotter Object within the scope of the method voidMethodCall
ScopedValue.runWhere(studentScopedValue, hp, RunnableClass::voidMethodCall);//using runnable, void method call

//binds studentScopedValue with harryPotter Object within the Supplier method voidMethodCall
ScopedValue.getWhere(studentScopedValue, hp, Class::supplierMethodCall);

For multiple scopes

// ScopedValues for managing different pieces of data
public static final ScopedValue<Student> studentScope = ScopedValue.newInstance();
public static final ScopedValue<Department> deptScope = ScopedValue.newInstance();

ScopedValue.where(studentScope, harrpPotter)
           .where(deptScope,gryffindor)
           .call(Class::method);

Get the Scoped Value

Return the value if bound, else return a default value

Student requestStudent = studentScopedValue.orElse(new Student("Harry Potter"));

Return the value if bound, else throw an exception

Student requestStudent = studentScopedValue.orElseThrow(() -> new RuntimeException("Not Bound");

Scoped values are not available for Child threads except the ones initiated with StructuredTaskScope

This is because threads started from StructuredTaskScope block are guaranteed to complete before the try-with-resources block ends and THUS remains within the scope of the ScopedValue.

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