JLD on Multithreading



I am calculating matrix entries through multithreading and now would like to save the matrix to a file because it gets too big for my RAM.

I read that the package JLD is most common for saving Julia variables.

But when I am now trying to save the multi threaded entries to a file:

using JLD
function test()
	save("test2.jld", "test", 1) #create file
	f = jldopen("test2.jld", "r+")
	Threads.@threads for i = 1:10
		for j = 1:10
			x = i + j
			write(f, "$i $j", x)

I get lots of errors, the first of them is:

Exception: EXCEPTION_ACCESS_VIOLATION at 0x6dad7bb7 – HDF5-DIAG: Error detected in HDF5 (1.8.13) at 0x6dad7bb7

I also tried to create a file for each matrix entry, but that did not work neither.

Does anyone know how to fix this or can recommend another way to save the matrix?

Thanks in advance


Writing in parallel to a single file is always dangerous, because those writes must be properly coordinated. I’m not sure if the Julia/JLD implementation does that. To be on the safe side, I suggest to serialize the writes. To do so, at the start of your function create a lock:

sl = Threads.SpinLock()

And then surround the write call with calls to lock and unlock:


In production code the call to write should probably be in a try block and the unlock call in a finally clause.


Okay, that works perfectly, thank you very much!