21. Why we use GPL and not LGPL for libjit

A common question about libjit is likely to be why we use the GNU General Public License instead of the GNU Lesser General Public License.

At its core, the issue is "Who are we helping gain extra value?". We wish to help the authors of other Free Software projects, as well as those who are working on Open Source projects with licenses that are compatible with the GPL. But we do not wish to help proprietary software companies without adequate compensation to the community.

Consider the following scenario: a proprietary software company devises a new programming language and a new virtual machine to go with it. However, their implementation isn't very compelling to customers because its bytecode interpreter is too slow.

If libjit was distributed under the terms of the LGPL, the company could link against the library and get a compelling implementation. This would increase the sale value of their software considerably. However, they wouldn't be compelled to give anything back to the Free Software community in exchange for this extra value.

Under the GPL, the company must either GPL their own code, write their own JIT from scratch, or negotiate a separate license with the authors of libjit. In the first instance, they give back to the community the value they have used. In the second instance, they neither give value to nor take value from the community. In the third instance, the authors are compensated for their work, which allows those authors to continue contributing Free Software to the community.

For more information on why we have taken this stance, please read the document "Why you shouldn't use the Library GPL for your next library" on the Free Software Foundation's Web site:

http://www.gnu.org/licenses/why-not-lgpl.html.

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