经过测试和源码分析，证实scrapy是单线程异步模式进行工作。

start t = 1421317312.693043 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/1

end t = 1421317312.693043 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/1

2015-01-15 02:21:52-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/1> (referer: None)

2015-01-15 02:21:52-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/2> (referer: None)

start t = 1421317312.697041 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/2

end t = 1421317312.697041 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/2

xxxxxxxxxxxxxxxxxxxxxxxxxxx

————parse t = 1421317312.699310 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/1

start t = 1421317370.153754 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/3

end t = 1421317370.153754 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/3

————parse t = 1421317370.156391 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/2

2015-01-15 02:22:50-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/3> (referer: None)

start t = 1421317370.171718 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/4

end t = 1421317370.171718 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/4

————parse t = 1421317370.175629 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/3

2015-01-15 02:22:50-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/4> (referer: None)

start t = 1421317370.194542 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/5

end t = 1421317370.194542 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/5

————parse t = 1421317370.197380 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/4

2015-01-15 02:22:50-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/5> (referer: None)

start t = 1421317370.213179 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/6

end t = 1421317370.213179 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/6

————parse t = 1421317370.216034 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/5

2015-01-15 02:22:50-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/6> (referer: None)

start t = 1421317370.230415 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/7

end t = 1421317370.230415 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/7

————parse t = 1421317370.233487 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/6

2015-01-15 02:22:50-0800 [dmoz] DEBUG: Crawled (200) <GET http://www.baidu.com/7> (referer: None)

start t = 1421317370.249530 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/8

end t = 1421317370.249530 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/8

————parse t = 1421317370.252307 thread id <property object at 0x7faab1e4be10>, http://www.baidu.com/7