guard !self.isEmpty else { return [] } // 如果数组为空就直接返回空数组

var result: [(Int, [T])] = []

let group = dispatch_group_create()

let syncQueue = dispatch_queue_create("com.gcd.kt", DISPATCH_QUEUE_SERIAL)

let subArrayLength: Int = max(1, self.count / NSProcessInfo.processInfo().activeProcessorCount / 2)

for var step = 0; step * subArrayLength < self.count; step++ {

var stepResult: [T] = []

let localStep = step

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {

for i in (localStep * subArrayLength)..<min(((localStep + 1) * subArrayLength), self.count) {

stepResult += [transform(self[i])]

}

dispatch_group_async(group, syncQueue) {

result += [(localStep, stepResult)]

}

}

}

dispatch_group_wait(group, DISPATCH_TIME_FOREVER)

return result.sort { $0.0 < $1.0 }.flatMap { $0.1 }