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Home » Extra libraries, Code snippets, applications etc. » U++ users applications in progress and useful code snippets, including reference examples! » Using CoFor with SSH package to parallelize sftp file downloads. (Example code)
Using CoFor with SSH package to parallelize sftp file downloads. [message #58802] Sun, 04 September 2022 22:34
Oblivion is currently offline  Oblivion
Messages: 1094
Registered: August 2007
Senior Contributor
Core/SSH package has some nice multithreading abilities which can be sometimes overlooked..

The code snippet below demonstrates a way to combine the MT capabilities of SSH package with Upp::CoFor (loop parallelization function):

1) It reads the content of a remote directory
2) Downloads multiple files with certain attributes in parallel, using the CoFor loop.

#include <Core/Core.h>
#include <Core/SSH/SSH.h>

using namespace Upp;

constexpr const char *path = "/pub/example/";
constexpr const int   MAXDOWNLOAD = 4;

CONSOLE_APP_MAIN
{
	StdLogSetup(LOG_COUT|LOG_FILE);
	// Ssh::Trace();
	
	SshSession session;
	if(!session.Timeout(10000).Compression().Connect("demo:password@test.rebex.net:22")) {
		RLOG(session.GetErrorDesc());
		return;
	}
	
	SFtp browser(session);
	SFtp::DirList ls;
	
	// Get a remote dir listing.
	if(!browser.ListDir(path, ls)) {
		RLOG(browser.GetErrorDesc());
		return;
	}

	// Filter the dir list.
	auto files =  FilterRange(ls, [](const SFtp::DirEntry& e) { return e.IsFile() && e.GetSize() <= 65536; });
	
	// Download the files, using worker threads in parallel.
	CoFor(min(files.GetCount(), MAXDOWNLOAD), [&](int i){
		const SFtp::DirEntry& e = files[i];
		String fpath = AppendFileName(path, e.GetName());
		RLOG("Downloading " << fpath);
		SFtp sftp(session);
		String file = sftp.LoadFile(fpath);
		if(sftp.IsError())
			RLOG(Format("Worker #%d: %s", sftp.GetId(), sftp.GetErrorDesc()));
		else
			RLOG("File " << e.GetName() << " is successfully downloaded.");
	});
}



Best regards,
Oblivion


[Updated on: Sun, 04 September 2022 22:49]

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