Advanced Multi-Threaded Development Overview

Explore the challenges and tips for developing multi-threaded applications in a workshop conducted by Jarrod Hollingworth in Melbourne. Learn about thread safety, Delphi Parallel Programming Library, and delve into low-level thread details. Dive into parallel programming with XE7+ and discover TParallel class functions for efficient multi-threaded execution. Gain insights into x86 Assembly and operations for optimizing CPU performance.

• Multi-Threaded Development
• Jarrod Hollingworth
• Thread Safety
• Delphi Programming
• Parallel Programming

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1. More! Multi-threaded Development Jarrod Hollingworth ADUG Melbourne, June 2018

2. Overview Threads Delphi Parallel Programming Library Thread Safety Challenges & Tips

3. Threads >= 1 per process Different CPUs in same process Share process resources (heap memory, globals, file handles) Own stack, program counter, registers Controlled by OS (time slice/wait, paused, resumed) Switched at any time Low level details are important

4. Parallel Programming Library XE7+, cross-platform System.Threading Based on TThread TParallel For loop, demo Basic thread safety Bonus demo: Conway s game of life TTask Running tasks, demo: Parallel Squares Waiting for task, demo Joins, futures, demo

5. TParallel class function For( LowInclusive: Integer; HighInclusive: Integer; IteratorEvent: TProc<Integer, TLoopState>; Sender: TObject; Stride: Integer; Pool: TThreadPool): TLoopResult; (30 overloads: optional parameters, anonymous methods/procedure of object, ) Iterations are run in parallel. Returns once all iterations are complete. TLoopState procedure Stop; procedure Break; property Stopped: Boolean; property Faulted: Boolean; TLoopResult property Completed: Boolean; property LowestBreakIteration: Integer; class function Join(const Procs: array of TProc; Pool: TThreadPool): ITask; (several overloads) Procedures are run in parallel. Returns once all procedures are complete.

6. x86 Assembly: total := total + 1; CPU1: CPU2: total mov edx,[eax+$0c] total inc edx mov [eax+$0c],edx total mov edx,[eax+$0c] inc edx mov [eax+$0c],edx total

7. x86 Operations: Inc(total); ASM: inc dword ptr [eax] CPU: Total Op.load temp_reg, [eax] Op.inc temp_reg Op.store [eax], temp_reg total

8. x86 Operations: Inc(total); ASM: inc dword ptr [eax] CPU2: CPU1: Op.load temp_reg, [eax] Op.inc temp_reg Op.store [eax], temp_reg Op.load temp_reg, [eax] Op.inc temp_reg Op.store [eax], temp_reg

9. TTask TTask class function Create/Run(Sender: TObject; Proc: TProc; APool: TThreadPool): ITask; class function WaitForAll(Tasks: array of ITask; Timeout: LongWord): Boolean; class function WaitForAny(Tasks: array of ITask; Timeout: LongWord): Integer; class function Future<T>(Sender: TObject; Func: TFunc<T>): IFuture<T>; ITask function Start: ITask; property Status: TTaskStatus; function Wait(Timeout: LongWord): Boolean; procedure Cancel; TTaskStatus Created, WaitingToRun, Running, Completed, WaitingForChildren, Canceled, Exception IFuture<T> property Value: T

10. TThreadPool TParallel.For/Join( , ThreadPool: ThreadPool) TTask.Create/Run( , ThreadPool: ThreadPool) TThreadPool is self-tuning based on # CPU cores and load Cannot free until all tasks are complete SetMaxWorkerThreads(Value: Integer) >= # CPU cores SetMinWorkerThreads(Value : Integer) <= MaxWorkerThreads Note: No guarantees. For total control use TThread.

11. Thread Safety Thread local variables (global storage) threadvar class threadvar Co-ordination & communication between threads (SyncObjs) TThread.Synchronize TThread.Queue (SyncObjs) TEvent.WaitFor(Timeout)/SetEvent/ResetEvent (Windows) PostMessage/SendMessage(Handle) (Windows) PostThreadMessage(ThreadId) Shared flag/data/queue, shared memory (inter-process), (immediate) (when main thread idle)

12. Thread Safety cont. Locking shared data/resource (SyncObjs) TCriticalSection.Acquire/Release/TryEnter (System) TMonitor.Enter(Obj, Timeout)/Exit/TryEnter: Boolean (SysUtils) TMultiReadExclusiveWriteSynchronizer BeginRead/EndRead/BeginWrite/EndWrite (SyncObjs) TSemaphore Create(InitialCount, AMaximumCount: Integer; Name: string) Acquire/Release(Count) (SyncObjs) TMutex.Create(Name: string)/Acquire/Release Atomic operations (SyncObjs) TInterlocked.Increment/Decrement/Add/Exchange/ (RTL) AtomicIncrement/ (Windows) InterlockedIncrement Fast Fast-ish, timeout Faster Slow, inter-process Slow, inter-process

13. Challenges & Tips Using the VCL/FMX & RTL Performance (different constraints, self tuning) Deadlocks (multiple locks, non re-entrant locks, use timeouts) Unhandled exceptions Testing (every computer/device and every run will be different) Stopping (or not) threads (notify, auto free, TerminateThread) Debugging (thread status, naming threads, switching threads) TThread.NameThreadForDebugging(Name: string)

14. Simple communication design Main thread Manager thread Data (locked) Job list UI Update Dispatch Synchronize/Queue/PostMessage Worker thread Worker thread Worker thread

15. Resources Book: Delphi High Performance - Primo Gabrijel i Wiki: http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Using_the_Parallel_Programming_Library Introduction video: https://youtu.be/x8S5b0peu7U Advanced techniques: http://web.archive.org/web/20120423060358/http://www.eonclash.com/Tutorials/Multithreading/ MartinHarvey1.1/ToC.html Demos: Conway s Life (TParallel.For) https://sourceforge.net/p/radstudiodemos/code/HEAD/tree/branches/RADStudio_Tokyo/Object%20 Pascal/RTL/Parallel%20Library/ Delphi Academy (Parallel Squares, TTask, Future) http://cc.embarcadero.com/Item/30754