var a = Array(repeating: 0, count: 10) let q = DispatchQueue(label: "array") DispatchQueue.concurrentPerform(iterations: 10) { i in q.sync { a[i] = i } } print(a) // [0, 1, ..., 9] と出て欲しい (edited)var a = Array(repeating: 0, count: 10) let q = DispatchQueue(label: "array") DispatchQueue.concurrentPerform(iterations: 10) { i in q.sync { a[i] = i } } print(a) // [0, 1, ..., 9] と出て欲しい (edited)