探讨php中error_log函数输出内容的原子性问题

PHPAPI int _php_error_log_ex(int opt_err, char *message, int message_len, char *opt, char *headers TSRMLS_DC) /* {{{ */
{
	php_stream *stream = NULL;

	switch (opt_err)
	{
		case 1:		/*send an email */
			if (!php_mail(opt, PHP error_log message, message, headers, NULL TSRMLS_CC)) {
				return FAILURE;
			}
			break;

		case 2:		/*send to an address */
			php_error_docref(NULL TSRMLS_CC, E_WARNING, TCP/IP option not available!);
			return FAILURE;
			break;

		case 3:		/*save to a file */
			stream = php_stream_open_wrapper(opt, a, IGNORE_URL_WIN | REPORT_ERRORS, NULL);
			if (!stream) {
				return FAILURE;
			}
			php_stream_write(stream, message, message_len);
			php_stream_close(stream);
			break;

		case 4: /* send to SAPI */
			if (sapi_module.log_message) {
				sapi_module.log_message(message TSRMLS_CC);
			} else {
				return FAILURE;
			}
			break;

		default:
			php_log_err(message TSRMLS_CC);
			break;
	}
	return SUCCESS;
}
/* }}} */

/* Writes a buffer directly to a stream, using multiple of the chunk size */
static size_t _php_stream_write_buffer(php_stream *stream, const char *buf, size_t count TSRMLS_DC)
{
	size_t didwrite = 0, towrite, justwrote;

 	/* if we have a seekable stream we need to ensure that data is written at the
 	 * current stream->position. This means invalidating the read buffer and then
	 * performing a low-level seek */
	if (stream->ops->seek && (stream->flags & PHP_STREAM_FLAG_NO_SEEK) == 0 && stream->readpos != stream->writepos) {
		stream->readpos = stream->writepos = 0;

		stream->ops->seek(stream, stream->position, SEEK_SET, &stream->position TSRMLS_CC);
	}


	while (count > 0) {
		towrite = count;
		if (towrite > stream->chunk_size)
			towrite = stream->chunk_size;

		justwrote = stream->ops->write(stream, buf, towrite TSRMLS_CC);

		/* convert justwrote to an integer, since normally it is unsigned */
		if ((int)justwrote > 0) {
			buf += justwrote;
			count -= justwrote;
			didwrite += justwrote;

			/* Only screw with the buffer if we can seek, otherwise we lose data
			 * buffered from fifos and sockets */
			if (stream->ops->seek && (stream->flags & PHP_STREAM_FLAG_NO_SEEK) == 0) {
				stream->position += justwrote;
			}
		} else {
			break;
		}
	}
	return didwrite;

}

 If the file was open(2)ed with <strong>O_APPEND</strong>, the file
       offset is first set to the end of the file before writing.  The
       adjustment of the file offset and the write operation are performed
       as an atomic step.

Atomic/non-atomic: A write is atomic if the whole amount written in one operation is not interleaved with data from any other process. This is useful when there are multiple writers sending data to a single reader. Applications need to know how large a write request can be expected to be performed atomically. This maximum is called {PIPE_BUF}. This volume of IEEE Std 1003.1-2001 does not say whether write requests for more than {PIPE_BUF} bytes are atomic, but requires that writes of {PIPE_BUF} or fewer bytes shall be atomic.

<!--?php

$str = ;
for($i = 0; $i < (int)$argv[2]; $i++)
{
    $str = $str.$argv[1];
}

for($i = 0; $i < (int)$argv[3]; $i++)
{
    error_log($str.
, 3, ./append.txt);
}

?-->

filename = ./append.txt

for line in open(filename):
    print len(line)

#!/bin/bash 

rm -f append.txt

for ((counter=0; counter < 10; ++counter))
do
    php test_error_log.php $counter $1 $2 &
done

sleep 2

#python check_line.py > a.txt

python check_line.py | sort | uniq -c