这两个bash并行化语法有什么区别？

Question

Value "4" below is the number of CPU threads. Idea is to run the tasks in batch of 4 and wait until the current batch is finished before starting the next batch.

Syntax 1:

while read something; do
((++i%4==0)) && wait
(
 task using something as input;
)
done < input_file.txt

Syntax 2:

while read something; do
((i=i%4)); ((i++==0)) && wait
(
 task using something as input;
)
done < input_file.txt

To me they both work the same except the second one is longer. But when running in the cloud (AWS ubuntu 14.04), only syntax 1 worked. The syntax2 threw a generic syntax error at "((i=i%4));" step and it became a mystery.

Answer 1

"The second one is longer" doesn't help since you used pseudocode.

Maybe this will help:

while read x; do ((i=++i%4)) || wait; sleep $x & done < input_file.txt

My input_file.txt :

10
9
8
7
6
5
4
3
2
1