XZOutputStream failes if preset is larger than 7

[ied206]

XZOutputStream throws an exception when its preset set to 8 or 9.
For detail, this exception is raised from XZOutputStream.cs line 83.

System.InsufficientMemoryException: 'Memory allocation failed'

It only happens if XZ.NET is using 32bit version of liblzma.dll, and it happens regardless of liblzma.dll's version (5.2.1 and 5.2.3 tested).

To reproduce, please use the test code from pull request #8 .

Tested Environment

• Windows 10 x64 v1709
• .Net Framework 4.7.1 installed
• XZ.NET 2.0 trageting .Net Framework 4 Client Profile

[ied206]

This error does not happen when argument 'threads' is set to 1 in XZOutputStream constructor.

[pentp]

The multi-threaded encoder creates separate encoding threads, each with its own memory allocation. With presets 8 or 9 it could easily use many gigabytes of memory, overflowing the 32-bit process address space limits.

I would recommend using a lower preset (faster, slightly lower compression ratio) or less threads (slower), depending on the use case.

[ied206]

I missed xz's large memory compression requirement, thanks for explaining.
My test environment has 8 threads which ends up 5392MB with preset 9.
Alloction about 5GB of memory would be impossible in Windows x86's 2GB userland memory restrict.