Yes, I have access to a C compiler.

You could rebuild having defined #define DEBUG_LOCKS at the top of shared.xs. The problem is then how to relate the addresses displayed:

 3e56088 waiting - owned by 3ef8c78 shared.xs:1032
 3e56088 waiting - owned by 3ef8c78 shared.xs:1136
 3e56088 waiting - owned by 3ef8c78 shared.xs:1208
 3e56088 waiting - owned by 3ef8c78 shared.xs:1265
 3e56088 waiting - owned by 3ef8c78 shared.xs:347
 3e56088 waiting - owned by 3ef8c78 shared.xs:520
 3e56088 waiting - owned by 3ef8c78 shared.xs:715
 3e56088 waiting - owned by 4001018 shared.xs:1032
 3e56088 waiting - owned by 4001018 shared.xs:1136
 3e56088 waiting - owned by 4001018 shared.xs:1208
 3e56088 waiting - owned by 4001018 shared.xs:1265
 3e56088 waiting - owned by 4001018 shared.xs:347
 3e56088 waiting - owned by 4001018 shared.xs:520
 3e56088 waiting - owned by 4001018 shared.xs:715
 3ef8c78 waiting - owned by 3e56088 shared.xs:1032
 3ef8c78 waiting - owned by 3e56088 shared.xs:1136
 3ef8c78 waiting - owned by 3e56088 shared.xs:1208
 3ef8c78 waiting - owned by 3e56088 shared.xs:1265
 3ef8c78 waiting - owned by 3e56088 shared.xs:347
 3ef8c78 waiting - owned by 3e56088 shared.xs:520
 3ef8c78 waiting - owned by 3e56088 shared.xs:715
 3ef8c78 waiting - owned by 4001018 shared.xs:1032
 3ef8c78 waiting - owned by 4001018 shared.xs:1136
 3ef8c78 waiting - owned by 4001018 shared.xs:1208
 3ef8c78 waiting - owned by 4001018 shared.xs:1265
 3ef8c78 waiting - owned by 4001018 shared.xs:347
 3ef8c78 waiting - owned by 4001018 shared.xs:520
 3ef8c78 waiting - owned by 4001018 shared.xs:715
 4001018 waiting - owned by 3e56088 shared.xs:1032
 4001018 waiting - owned by 3e56088 shared.xs:1136
 4001018 waiting - owned by 3e56088 shared.xs:1208
 4001018 waiting - owned by 3e56088 shared.xs:1265
 4001018 waiting - owned by 3e56088 shared.xs:347
 4001018 waiting - owned by 3e56088 shared.xs:520
 4001018 waiting - owned by 3e56088 shared.xs:715
 4001018 waiting - owned by 3ef8c78 shared.xs:1032
 4001018 waiting - owned by 3ef8c78 shared.xs:1136
 4001018 waiting - owned by 3ef8c78 shared.xs:1208
 4001018 waiting - owned by 3ef8c78 shared.xs:1265
 4001018 waiting - owned by 3ef8c78 shared.xs:347
 4001018 waiting - owned by 3ef8c78 shared.xs:520
 4001018 waiting - owned by 3ef8c78 shared.xs:715
[download]

Back to either thread ids or thread handles:

tid 3 : handle: 4065f20
tid 2 : handle: 3fd9810
tid 1 : handle: 3f393b0
[download]

The "trick" would be unravelling the defnition of aTHX, but I've never gotten to the bottom of that piece of tortuous magic.