threads doc's have two potentially interesting things to say, that may just help.

firstly, you seem to missing a semicolon or two.

async BLOCK;
        "async" creates a thread to execute the block immediately foll
+owing
        it. This block is treated as an anonymous subroutine, and so m
+ust have
        a semicolon after the closing brace.
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also

Threads are implemented in a way that make them easy to misuse.
Few people know how to use them correctly or will be able to provide h
+elp.

The use of interpreter-based threads in perl is officially discouraged
+.
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