1. Martin Kruliš 14. 1. 2016 by Martin Kruliš (v1.1)1

2.  Massively Distributed Systems ◦ Computing grids using Internet (e.g., BOINC) ◦ Millions of PCs offering their computational power  Major Issues ◦ Security  Implicit trust in the code the clients are running  Vulnerable to sabotage ◦ Accessibility (complexity of client installation) ◦ Works for specific problems only  With heavy computations and small data transfers 14. 1. 2016 by Martin Kruliš (v1.1)2

3.  Web Browser as a Computing Platform ◦ Recent development in web technologies  JavaScript and new HTML5 features  Parallel execution (web workers, webCL)  Communication (Asynchronous HTTP, WebSockets)  Advantages ◦ Trivial usage, no (additional) installation required  Everyone has/uses web browser these days ◦ Implicit security provided by the browser  Disadvantages ◦ Potential for parasitic computing systems 14. 1. 2016 by Martin Kruliš (v1.1)3

4.  Web Workers ◦ API, which is part of new HTML5 technologies ◦ Worker represents separate computing thread  The code of the worker is sandboxed  API for bidirectional communication with main thread  Workers may spawn sub-workers ◦ API  Worker(url) – constructing function  Worker.postMessage(msg) – send message to the peer  Worker.onmessage – receiving message event handler  Worker.terminate() – kill the worker thread 14. 1. 2016 by Martin Kruliš (v1.1)4 Example 1

5.  WebCL ◦ JavaScript binding for OpenCL API  Allows access to multicore CPUs and GPUs  Implemented in window.WebCL interface ◦ Currently no browser natively implements WebCL  Plugins exist for majority of browsers ◦ Important issues  OpenCL device/host synchronization is often performed by blocking operations  Callbacks should be used in WebCL instead  Explicit object releasing is required due to dynamic nature of JS (managed memory and garbage collector) 14. 1. 2016 by Martin Kruliš (v1.1)5 Example 2

6. 14. 1. 2016 by Martin Kruliš (v1.1)6