$ ./t_file_queue.pl 
1.txt: opened new file (1)
1.txt: (cnt=2) found
2.txt: opened new file (3)
1.txt: (cnt=4) found
2.txt: (cnt=5) found
2.txt: (cnt=6) found
3.txt: opened new file (7)
2.txt: (cnt=8) found
2.txt: (cnt=9) found
3.txt: (cnt=10) found
4.txt: Too many open files, close one: 1.txt:4, 2.txt:9, 3.txt:10
   closing 1.txt
4.txt: opened new file (11)
1.txt: Too many open files, close one: 2.txt:9, 3.txt:10, 4.txt:11
   closing 2.txt
1.txt: opened new file (12)
1.txt: (cnt=13) found
1.txt: (cnt=14) found
1.txt: (cnt=15) found
5.txt: Too many open files, close one: 3.txt:10, 4.txt:11, 1.txt:15
   closing 3.txt
5.txt: opened new file (16)