File segment/section/record locks in Linux threads

Question

I have a multi-threaded process where a file is shared (read and written) by multiple threads. Is there any way a thread can lock one file segment so that other threads cannot a

Answer 1

Yes - but not with the same mechanism. You'll have to use something like pthread mutexes, and keep track of the bookkeeping yourself.

Possible outline for how to make this work

• Wait on and claim a process-level mutex over a bookkeeping structure
  • make sure no other threads within your process are trying to use that segment
  • mark yourself as using the file segment

• Release the process-level mutex

• Grab fnctl lock for process (if necessary)

• Do your writing

• Release fnctl lock to allow other processes to use the segment (if necessary)

• Wait again on process-levelbookkeeping structure mutex (may not be necessary if you can mark it unused atomically)

  • mark segment as unused within your process.
• Release process-level mutex