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von_weiqiang木蟲 (正式寫手)
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[求助]
用MPICH2運(yùn)行并行程序,代碼中的printf語(yǔ)句只有在所有進(jìn)程都結(jié)束后才會(huì)打印出來(lái)么? 已有2人參與
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能不能各進(jìn)程一邊運(yùn)行,一邊打? 例如代碼: MPI_Init(&argc, &argv); MPI_Comm_rank(MPI_COMM_WORLD,&myrank); for(i=0;i<1e1;i++) { a=integration(0,1,1e-6,f); printf("current %d %d %e\n",myrank,i,a); } MPI_Finalize(); 其中,integration函數(shù)每調(diào)用一次需要約2s時(shí)間,每個(gè)進(jìn)程運(yùn)行時(shí)間大約20s,我的理解是,每個(gè)進(jìn)程每2s就應(yīng)該打印一次“進(jìn)程號(hào),循環(huán)次數(shù)”,所以進(jìn)程號(hào)應(yīng)該是雜亂無(wú)章的,可是用MPICH開啟3個(gè)進(jìn)程實(shí)際運(yùn)行結(jié)果是這樣: current 0 0 3.141593e+000 current 0 1 3.141593e+000 current 0 2 3.141593e+000 current 0 3 3.141593e+000 current 0 4 3.141593e+000 current 0 5 3.141593e+000 current 0 6 3.141593e+000 current 0 7 3.141593e+000 current 0 8 3.141593e+000 current 0 9 3.141593e+000 current 2 0 3.141593e+000 current 2 1 3.141593e+000 current 2 2 3.141593e+000 current 2 3 3.141593e+000 current 2 4 3.141593e+000 current 2 5 3.141593e+000 current 2 6 3.141593e+000 current 2 7 3.141593e+000 current 2 8 3.141593e+000 current 2 9 3.141593e+000 current 1 0 3.141593e+000 current 1 1 3.141593e+000 current 1 2 3.141593e+000 current 1 3 3.141593e+000 current 1 4 3.141593e+000 current 1 5 3.141593e+000 current 1 6 3.141593e+000 current 1 7 3.141593e+000 current 1 8 3.141593e+000 current 1 9 3.141593e+000 請(qǐng)按任意鍵繼續(xù). . . 為什么呢? |

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這個(gè)問(wèn)題設(shè)計(jì)計(jì)算機(jī)的緩沖區(qū)。print的東西是先輸出到緩沖區(qū),再?gòu)木彌_區(qū)輸出到終端的(文件,或者顯示器)。所以最終的輸出和系統(tǒng)有關(guān)系,并不能直接反應(yīng)運(yùn)行順序。你可以使用flush命令來(lái)刷新緩沖區(qū),并用mpi_barrier()來(lái)同步各個(gè)進(jìn)程,就可以得到想要的順序。 [ 發(fā)自手機(jī)版 http://www.gaoyang168.com/3g ] |

木蟲 (正式寫手)

銀蟲 (初入文壇)
木蟲 (文壇精英)

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