search

littlefs-project / littlefs

A little fail-safe filesystem designed for microcontrollers
BSD 3-Clause "New" or "Revised" License
5.22k stars 799 forks source link

reentrency (read file while write) #124

Open ranshalit opened 6 years ago

ranshalit commented 6 years ago

Hello,

I am using littlefs with freertos (nxp sdk). Is it allowed to read file while another task is writing into the same file ?

Thank you, ranran

cfr-mir commented 5 years ago

Ranran,

I am using littleFS with FreeRTOS.

My experience are, Multible readers are OK, but writers must be alone.

If reads are occuring while a file are open for write, you will have bad data written into your file.

Regards Carsten

geky commented 5 years ago

Hi, sorry for late response.

littlefs has no locking of its own, if you use littlefs in multiple threads you will need to lock each call with your own mutex (in mbed-os for example).

But if you add locks both multiple readers and writers should work.

The fact that multiple lockless readers works is probably luck due to the fact that reads don't change much state. I'm not sure it will work if files span multiple blocks.

cfr-mir commented 5 years ago

Geky and Ranran, Sorry for not beeing super precise. Of course you must have a mutex protection around all calls to LittleFS. I have that. In the meantime I have investigated my concurrent write/read problem. And It originates from newlibs filestream implementation, which according to specs should be reentrant (With the proper mutexes implemented).

So LittleFS do support multiple open files reading and writing, as long as you keep a mutex around calls to LittleFS. Geky you knew that.

Best regards Carsten