MultiThread Introduction

MultiThread Introduction

Win32 • function • CreateThread • Ex: • thread = CreateThread(NULL,0,Threadfun,(LPVOID)param,0,&threadId);

Win32 • function • WaitForMultipleObjects • Ex: • WaitForMultipleObjects(c_size ,work_thread,TRUE,INFINITE);

Win32 • Function • CloseHandle • Ex: • CloseHandle(work_thread[i]);

CRT or MFC • C Run-Time Library • _beginthreadex • MFC • AfxBeginThread

Code for(i=0;i<c_size;i++){ work_thread[i]=CreateThread(NULL,0,calculate,(LPVOID)i,0,&work_threadId[i]); } WaitForMultipleObjects(c_size ,work_thread,TRUE,INFINITE); //all done ,then close for(i=0;i<c_size;i++){ CloseHandle(work_thread[i]); }

Code DWORD WINAPI calculate(LPVOID x) { int i,j,k; int value=0; i = (int)x/C_columSize; j = (int)x%C_columSize; for (k=0; k<A_columSize ; k++){ value += A[i*A_columSize + k] * B[k*B_columSize + j]; } return C[(int)x] =value; }

Note • 考慮 • Race condition • Deadlock • 設計 • Variable independent • Iterative • Load balance

Crawler • Class Crawler: • 執行整個抓取頁面的邏輯。 • Class ContextStorage: • 讀取頁面到記憶體並進行相關處理和操作URL如儲存連結，擷取連結。 • Class URLManager: • 儲存連結的一個資料結構，確保連結不重複並可回傳下一連結。(樹狀結構，每一個node儲存某一頁面的所有連結。另外用MAP儲存所有連結，辨識是否重複。) • Class FileManager: • 負責將內文依照設定的方式存入硬碟。

Crawler

Open Multi-Processing API • OpenMP • Wiki • The OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C/C++ and Fortran on many architectures, including Unix and Microsoft Windows platforms. • Ex: #pragma omp parallel { #pragma omp for for(int i = 1; i < size; ++i) x[i] = (y[i-1] + y[i+1])/2; }

Site: • OpenMP and C++ Reap the Benefits of Multithreading without All the Work • [Heresy' Space]: 簡易的程式平行化方法－OpenMP（一）簡介

MultiThread Introduction