CODEWITHSUNDEEP
mpitiff
ziv
ziv

Reputation: 189

MPI parallel write to a TIFF file

I'm trying to write a TIFF file in MPI code. Different processors have different parts of the image, and I want to write the image to the file in parallel.

The write fails, only the 1st processor can write to it.

How do I do this?

There is no error in my implementation, just it does not work.
I used h=TIFFOpen(file, "a+") on each processor to open the same file (I am not sure whether this is a right way or not), then each processor who is responsible for a directory will write the header at its own place using TIFFSetDirectory(h, directorynumber), then the content of each directory will be written. I will finalize with TIFFWriteDirectory(h). The result would be the first directory which is written on the file.

I thought that I need to open the file using MPI_IO but doing this way it is not TIFFOpen?

Upvotes: 2

Views: 584

Answers (1)

Sigi
Sigi

Reputation: 4926

Different MPI tasks are independent programs, running on independent hosts from the OS point of view. In your case the TIFF library is not designed to handle parallel operations, so opening the file will lead the first process to succeed, all the rest to fail because they found the file already opened (on a shared filesystem).

Except in case you are dealing with huge images (eg: astronomical images) where it's important for performance to perform parallel I/O (you need a filesystem supporting it however... I am aware of IBM GPFS), I would avoid to write a custom TIFF driver with MPI_IO.

Instead the typical solution is to gather (MPI_Gather()) the image parts on the process with rank==0 and let it only save the tiff file.

Upvotes: 2

Related Questions