纵轴表示访问列表/数组中每个节点的平均时间(以ns为单位)(访问所有元素所需的总时间除以元素数量)。
横轴表示正在迭代的数组中的元素数量。
其中红色是NSMutableArray
的实现,蓝色是我的链表(CHTape
)。
在每个外部循环中,每个列表/数组都会添加一个空字符串@""
。在内部循环中,检索每个列表/数组中的字符串,计时并记录。最后,输出时间以产生Wolfram语言输出以生成绘图。
NSMutableArray
如何实现如此出色和一致的结果?如何才能达到类似的效果?
我的NSFastEnumeration实现:
- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id __unsafe_unretained [])stackBuffer count:(NSUInteger)len
{
if (state->state == 0)
{
state->state = 1;
state->mutationsPtr = &state->extra[1];
state->extra[0] = (unsigned long)head;
}
CHTapeNode *cursor = (__bridge CHTapeNode *)((void *)state->extra[0]);
NSUInteger i = 0;
while ( cursor != nil && i < len )
{
stackBuffer[i] = cursor->payload;
cursor = cursor->next;
i++;
}
state->extra[0] = (unsigned long)cursor;
state->itemsPtr = stackBuffer;
return i;
}
完整的测试代码:
NSMutableArray *array = [NSMutableArray array];
CHTape *tape = [CHTape tape];
unsigned long long start;
unsigned long long tapeDur;
unsigned long long arrayDur;
NSMutableString * tapeResult = [NSMutableString stringWithString:@"{"];
NSMutableString * arrayResult = [NSMutableString stringWithString:@"{"];
NSString *string;
int iterations = 10000;
for (int i = 0; i <= iterations; i++)
{
[tape appendObject:@""];
[array addObject:@""];
// CHTape
start = mach_absolute_time();
for (string in tape){}
tapeDur = mach_absolute_time() - start;
// NSArray
start = mach_absolute_time();
for (string in array){}
arrayDur = mach_absolute_time() - start;
// Results
[tapeResult appendFormat:@"{%d, %lld}", i, (tapeDur/[tape count])];
[arrayResult appendFormat:@"{%d, %lld}", i, (arrayDur/[array count])];
if ( i != iterations)
{
[tapeResult appendString:@","];
[arrayResult appendString:@","];
}
}
[tapeResult appendString:@"}"];
[arrayResult appendString:@"}"];
NSString *plot = [NSString stringWithFormat:@"ListPlot[{%@, %@}]", tapeResult, arrayResult];
NSLog(@"%@", plot);