title: MATLAB parfor 进度的提取
date: 2019-03-03 01:31:38
tags:
MATLAB
并行计算
categories:
- 技术
MATLAB parfor 进度显示
用MATLAB的时候，经常会用到并行计算，用于加快速度。我们有时候还需要知道程序具体运行到哪一步，比如循环一个有100个，已经运行了多少个。如果不是parfor,我们可以采用每进行一次运算，就输出一些信息到文件的方法，比如
N=10;
fid=fopen('progress.txt','at');
for l=1:
fprintf(fid,[datestr(now),' the loop step is %d \n'],l);
end
fclose(fid);
这样的话，就会在程序里面输出每一个循环已经执行的信息。可以看见输出的txt文件夹具有如下的内容：
02-Mar-2019 23:50:17 the loop step is 1
02-Mar-2019 23:50:17 the loop step is 2
02-Mar-2019 23:50:17 the loop step is 3
02-Mar-2019 23:50:17 the loop step is 4
02-Mar-2019 23:50:17 the loop step is 5
02-Mar-2019 23:50:17 the loop step is 6
02-Mar-2019 23:50:17 the loop step is 7
02-Mar-2019 23:50:17 the loop step is 8
02-Mar-2019 23:50:17 the loop step is 9
02-Mar-2019 23:50:17 the loop step is 10
上面的
datestr(now)
可以得到当前的时间。这是对于普通循环的用法，如果是parfor呢？因为并行计算会调用多个cpu进行计算，此时如果接着用上面的命令，就会出现多个内核同时对同一个文件处理，在服务器上面计算就会因为文件权限问题报错
错误使用 parfor_matlab (line 3)
文件标识符无效。使用 fopen 生成有效的文件标识符。
为了避免这种错误，我们可以将上面的对文件的操作放在parfor里面，即
N=10;
parfor l=1:
fid=fopen('progress.txt','at');
fprintf(fid,[datestr(now),' the loop step is %d \n'],l);
fclose(fid);
end
这样每次运行出一个结果，就可以输出一个结果到文件，且不会相互冲突。还需要注意的是，我们这里输出的结果不是按顺序的，而是不同cpu计算的结果随机填充到文件里面,我们必须手动数一数输出了几行结果到文件里面了，如下。
03-Mar-2019 00:02:45 the loop step is 10
03-Mar-2019 00:03:03 the loop step is 4
03-Mar-2019 00:03:03 the loop step is 7
03-Mar-2019 00:03:03 the loop step is 1
03-Mar-2019 00:03:03 the loop step is 3
03-Mar-2019 00:03:03 the loop step is 6
03-Mar-2019 00:03:03 the loop step is 5
03-Mar-2019 00:03:03 the loop step is 2
03-Mar-2019 00:03:03 the loop step is 8
03-Mar-2019 00:03:03 the loop step is 10
03-Mar-2019 00:03:03 the loop step is 9
可以看见，上面的结果是随机的，为了具体知道到底计算了几个循环了，有两个办法，一是用文本编辑器打开txt文件，一般都会在左边显示行数，数有几行，就可以知道计算了几个了。第二个方法是我们可以再次读取一下我们的txt文件，数一数其矩阵的大小，就可以知道具体计算了多少行了。代码如下
%每次运行确保文件‘progress_1.txt'，‘progress_2.txt'都是空的
N=10;
for l=1:N
%首先输出一个运行循环的结果到'progress_1.txt'文件
fid=fopen('progress_1.txt','a');
fprintf(fid,[datestr(now),' the loop step is %d \n'],l);
fclose(fid);
%然后从'progress_1.txt'文件读取文件的字符长度
fid=fopen('progress_1.txt','r');
[A, count]=fscanf(fid,'%s');%count是读取字符的个数，我们每一行都有7个字符，所以count是7的倍数
fclose(fid);
fid=fopen('progress_2.txt','a');
%最后在另外一个文件输出我们的总共计算了多少步
fprintf(fid,[datestr(now),' has looped for %d steps \n'],count/7);
fclose(fid);
end
这样就可以在文件里面实时查看我们的计算进度了。这样的坏处是由于我们频繁读取文件，运行速度会变慢，对于每一个parfor循环都需要很久的情况，这种方法是值得一试的。前面讲的都是在非图形界面的情况，如果我们有图形界面，其实还有更加好的解决方法，可以一边计算，一边显示百分比。在matlab的英文社区搜索“parfor progressbar”，就会有很多的结果，下面我展示一个我认为最好的解决方法，不需要额外的java之类的,我们需要将下面这段代码保存为“parfor_progressbar_v1.m”，和要计算的代码放在同一个文件夹，计算时候调用即可。下面也已经有了调用的例子。
classdef parfor_progressbar_v1 < handle
% PARFOR_PROGRESSBAR Progress bar suitable for multi-process computation.
%
% H = parfor_progressbar(N, 'message', 'property',value, ...)
% creates a graphical progress bar with N iterations before completion.
% A temporary file in tempdir is used to communicate among threads.
% Any property/value pairs are passed to waitbar internally (optional).
%
% H.iterate(X) updates the progress bar by X iterations.
%
% Example:
% --------
% N=50; %total number of parfor iterations
% hbar = parfor_progressbar(N,'Computing...'); %create the progress bar
% parfor i=1:N,
% pause(rand); % computation
% hbar.iterate(1); % update progress by one iteration
% end
% close(hbar); %close progress bar
%
% Notes:
% ------
% Properties cannot be modified while inside a parfor loop. Use iterate only.
%
% With many short iterations, call iterate() periodically. Example:
% if mod(i,10)==0, hbar.iterate(10); end
%
% Inspired by the parfor_progress script made by Jeremy Scheff:
% http://www.mathworks.com/matlabcentral/fileexchange/32101
%
% See also: WAITBAR, PARFOR.
% Copyright 2015-2016 Cornell University All Rights Reserved.
% Public properties
properties (SetAccess=protected, GetAccess=public)
wbh; % Waitbar figure object handle
N; % Total number of iterations expected before completion
Msg;
end
properties (Dependent, GetAccess=public)
percent; % Percentage of completed iterations
end
properties (Dependent, SetAccess=public, GetAccess=public)
message; % Message text displayed in waitbar
end
% Internal properties
properties (SetAccess=protected, GetAccess=protected, Hidden)
ipcfile; % Path to temporary file for inter-process communication
htimer; % Timer object that checks ipcfile for completed iterations
end
methods
%======================== CONSTRUCTOR ========================%
function this = parfor_progressbar_v1(N_init, varargin)
% Create a new progress bar with N_init iterations before completion.
% Create a unique inter-process communication file.
for i=1:10
f = sprintf('%s%d.txt', mfilename, round(rand*1000));
this.ipcfile = fullfile(tempdir, f);
if ~exist(this.ipcfile,'file'), break; end
end
if exist(this.ipcfile,'file')
error('Too many temporary files. Clear out tempdir.');
end
% Create a new waitbar
this.N = N_init;
this.Msg = varargin{1};
this.wbh = waitbar(0, [this.Msg, '0% Complete']);
% Create timer to periodically update the waitbar in the GUI thread.
this.htimer = timer( 'ExecutionMode','fixedSpacing', 'Period',0.5, ...
'BusyMode','drop', 'Name',mfilename, ...
'TimerFcn',@(x,y)this.tupdate );
start(this.htimer);
end
%========================= DESTRUCTOR ========================%
function delete(this)
this.close();
end
function close(this)
% Closer the progress bar and clean up internal state.
% Stop the timer
if isa(this.htimer,'timer') && isvalid(this.htimer)
stop(this.htimer);
pause(0.01);
delete(this.htimer);
end
this.htimer = [];
% Delete the IPC file.
if exist(this.ipcfile,'file')
delete(this.ipcfile);
end
% Close the waitbar
if ishandle(this.wbh)
close(this.wbh);
end
this.wbh = [];
end
%====================== GET/SET METHODS ======================%
function percent = get.percent(this)
% Calculate the fraction of completed iterations from IPC file.
if ~exist(this.ipcfile, 'file')
percent = 0; % File may not exist before the first iteration
else
fid = fopen( this.ipcfile, 'r' );
percent = sum(fscanf(fid, '%d')) / this.N;
percent = max(0, min(1,percent) );
fclose(fid);
end
end
function set.message(this, newMsg)
% Update the progress bar's displayed message.
if ishandle(this.wbh)
waitbar( this.percent, this.wbh, newMsg );
end
end
function iterate(this, Nitr)
% Update the progress bar by Nitr iterations (or 1 if not specified).
if nargin<2, Nitr = 1; end
fid = fopen(this.ipcfile, 'a');
fprintf(fid, '%d\n', Nitr);
fclose(fid);
end
end %public methods
%===================== INTERNAL METHODS =====================%
methods (Access=protected, Hidden)
function tupdate(this)
% Check the IPC file and update the waitbar with progress.
if ishandle(this.wbh)
waitbar( this.percent, this.wbh, sprintf('%s...%2.0f%% complete', this.Msg, this.percent*100));
else
% Kill the timer if the waitbar is closed.
close(this);
end
end
end %private methods
end %classdef
