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A state abstraction for Java

A state abstraction for Java. Ferruccio Damiani, Paola Giannini, Sophia Drossopoulou, Nick Cameron, Elena Giachino Presentation by Nick Cameron ncameron@doc.ic.ac.uk Imperial College London. Implicit state. Object a. Object a. m. m. m(). Some internal change. time. { while (…) {

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A state abstraction for Java

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  1. A state abstraction for Java Ferruccio Damiani, Paola Giannini, Sophia Drossopoulou, Nick Cameron, Elena Giachino Presentation by Nick Cameron ncameron@doc.ic.ac.uk Imperial College London

  2. Implicit state Object a Object a m m m() Some internal change time Nicholas Cameron DoC Imperial College 2006

  3. { while (…) { try { this.wait(); } catch (…) {…} } … } { … this.notifyAll(); } Implicit state • Hard to program • Non-intuitive • Lack of abstraction • Error prone • Missed statements • Boilerplate • Mixes functionality with coordination code Nicholas Cameron DoC Imperial College 2006

  4. Explicit state Object a Object a s1 s1 m1() m1 m1 s2 s2 m2() m2 m2 as2 time Nicholas Cameron DoC Imperial College 2006

  5. StateJ class C { String f1; state s1 { void m1() {…} } state s2 { void m1() {…} void m2() {…} } void m3() {…} } Nicholas Cameron DoC Imperial College 2006

  6. StateJ { this!!s2; this!!previous; } state s2 { void m() as s1 } Nicholas Cameron DoC Imperial College 2006

  7. Case studies Java, StateJ, Chords Buffer reader/writer lock Latch Santa Claus problem Submarine Radar problem … Class Buffer { state full { void put(Object o) as partial } state empty { Object get() as partial } state partial { void put (Object o) {…} Object get() {…} } } Programming with StateJ Nicholas Cameron DoC Imperial College 2006

  8. Implementation and Formal System • Formal system extends Featherweight Java • Multiple threads • States, state change statement, spawn statement • Type sound • Implementation - compiler • Compiles (large) subset of Java + states to Java • Inheritance Nicholas Cameron DoC Imperial College 2006

  9. Current work • States can have fields state s1 (int n) {…} this!!s1(x); • Effect system to ensure fields are not accessed outside the correct state • Improving the StateJ compiler • Further case studies Nicholas Cameron DoC Imperial College 2006

  10. Conclusion • Explicit states makes it easier to write concurrent programs. • Objects have state, method dispatch depends on current state. • Type safe formal system and compiler. • Ongoing work… Nicholas Cameron DoC Imperial College 2006

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