Crash on multithreaded execution

[bademux]

Lib crashed when execute on > 1 thread something like this

 executor.execute(() -> {
		try (FileChannel ch = FileChannel.open(path, READ);
			 VipsImage image = new VipsImage(ch.map(READ_ONLY, 0, ch.size()), (int) ch.size())) {
			image.resize(new Dimension(300, 300), true)
		}});

[dbouron]

What is the format of the test image? Does is crash with a SIGSEGV?

[bademux]

Any jpeg (I have some pngs and gifs, but mostly jpegs)
It crashed as SIGSEGV.
Single thread is OK.
Tested on linux with 2 and 4 threads - hard crash.

[dbouron]

I can reproduce using an ExecutorService with a CompletionService.
We aren't using byte buffers in production but byte arrays where we haven't any crash in MT context.
I will have a look when I have the time.

[dbouron]

I suspect an early FileChannel closing in the try-with resources statement which unmaps the memory.
The JVM seems to crash after unmap.

In command line, it sometimes throws several CloseChannelException instead of sigsegv.
Moreover, I see several unmap() calls with stace before the crash.

[bademux]

Hi, thanks for investigating the problem!
Maybe it is worth to change JVips API to prevent unmap problems?

[dbouron]

I will have a look how to handle this case and what is possible to do