procfile is a library for reading text data files (i.e
/proc files) in the fastest possible way.
How it works¶
The library automatically adapts (through the iterations) its memory so that each file
is read with single
Then the library splits the file into words, using the supplied separators. The library also supported quoted words (i.e. strings within of which the separators are ignored).
Initially the caller:
procfile_open()to open the file and allocate the structures needed.
For each iteration, the caller:
procfile_readall()to read updated contents. This call also rewinds (
lseek()to 0) before reading it.
For every file, a BUFFER is used that is automatically adjusted to fit
the entire file contents of the file. So the file is read with a single
(providing atomicity / consistency when the data are read from the kernel).
Once the data are read, 2 arrays of pointers are updated:
wordsarray, pointing to each word in the data read
linesarray, pointing to the first word for each line
This is highly optimized. Both arrays are automatically adjusted to fit all contents and are updated in a single pass on the data.
The library provides a number of macros:
procfile_lines()returns the # of lines read
procfile_linewords()returns the # of words in the given line
procfile_word()returns a pointer the given word #
procfile_line()returns a pointer to the first word of the given line #
procfile_lineword()returns a pointer to the given word # of the given line #
When the caller exits:
procfile_free()to close the file and free all memory used.
- a raspberry Pi 1 (the oldest single core one) can process 5.000+
/procfiles per second.
- a J1900 Celeron processor can process 23.000+
/procfiles per second per core.
To achieve this kind of performance, the library tries to work in batches so that the code and the data are inside the processor’s caches.
This library is extensively used in netdata and its plugins.