Re: [RFC \ WISH] Add -o option to git-rev-list

["Marco Costalba" <mcostalba@gmail.com>]

On 12/10/06, Linus Torvalds <torvalds@osdl.org> wrote:
>

> data into ASCII etc. So temp-files are almost never a better solution than
> keeping things in memory (unless you use those temp-files to truly
> _share_ data between processes, ie you do a shared mmap and they can
> re-use the same pages actively in a way they couldn't otherwise).
>

Ok. Perhaps I'm doing something wrong but the following code it's
always 10% slower then the temporary file one (4.7s against 4.3s for
linux tree)

bool DataLoader::start(const QStringList& args, const QString& workDir) {

	QDir::setCurrent(workDir);

	_file = popen(args.join(" ").ascii(), "r");
	if (!_file)
		return false;
	
	loadTime.start();
	guiUpdateTimer.start(10, true); // will call on_timeout() in 10ms
	return true;
}

void DataLoader::on_timeout() {

	if (canceling)
		deleteLater();

// 	int fd = fileno(_file);    // read() case

	ssize_t len = 0;
	while (1) {

		QByteArray* ba = new QByteArray(FILE_BLOCK_SIZE); // 64KB

// 		len = read(fd, ba->data(), ba->size());        // read() case

		len = fread(ba->data(), 1, ba->size(), _file); // fread() case
		if (len <= 0) {
			delete ba;
			break;

		} else if (len < (ssize_t)ba->size()) // very rare, 4 out of 40000
on Linux tree
			ba->resize(len);

		loadedBytes += len;
		fh->rowData.append(ba); // fh->rowData it's a pointer's list
		parseSingleBuffer(ba);

		// avoid reading small chunks if data producer is still running
		if (len < FILE_BLOCK_SIZE)
			break;
	}

// 	if (len == 0) {         // read() case
	if (feof(_file)) {      // fread() case
	
		emit loaded(fh, loadedBytes, loadTime.elapsed(), true, "", ""); //
show some stats

		pclose(_file);
		_file = NULL;
		deleteLater();
	} else
		guiUpdateTimer.start(100, true); // next read in 100ms	
}

Uncomment 'read() case' lines and comment out the 'fread case()' ones
and you have a way slooooower code, about 10 times slower!