[PHP kernel] Some situations----file system functions for normal files _php tutorial

Today and colleagues to discuss the role of the Fflush function, the PHP file system function should be built on the system's standard I/O library, so, arbitrarily think that the role of fflush is to brush out the standard I/O library buffer, equivalent to the standard I/O library fflush function ....

Later followed the code, found that the results are very different ...

Let's start with the results:

1. The file system functions in PHP (fopen, fwrite, fread, fseek, etc.) are used internally by system calls such as open, write, read, Seek, and so on, without a standard I/O library.

2. The Fflush function does not have any effect when applied to ordinary files.

Tracking process:

From the ext/standard/file.c.

Php_named_function (Php_if_fopen)

As a portal, we finally found the following definition in MAIN/STREAMS/PLAIN_WRAPPER.C

Phpapi Php_stream_ops php_stream_stdio_ops = {

Php_stdiop_write, Php_stdiop_read,

Php_stdiop_close, Php_stdiop_flush,

"STDIO",

Php_stdiop_seek,

Php_stdiop_cast,

Php_stdiop_stat,

Php_stdiop_set_option

};

This is the underlying implementation of the main file system functions applied on ordinary files

Take Php_stdiop_flush (fflush for PHP User Configuration) as an example:

static int Php_stdiop_flush (Php_stream *stream tsrmls_dc)

{

Php_stdio_stream_data *data = (php_stdio_stream_data*) stream->abstract;

ASSERT (data! = NULL);

/*

* Stdio buffers data in the user land. by calling Fflush (3), this

* Data is send to the kernel using write (2). Fsync ' ing is

* Something completely different.

*/

if (data->file) {

Return Fflush (Data->file);

}

return 0;

}

While the ordinary files in the initialization process (can be seen during the process of tracking open), is not set data->file this field, but the use of data->fd ....

So fflush is not called here, that is, when fflush is used in ordinary files, it has no effect.

AUTHOR:SELFIMPR mail:lgg860911@yahoo.com.cn

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