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select、poll、epoll之间的区别总结[整理] - C/C++ - 清泛网 - 专注C/C++及内核技术
...1、select实现
select的调用过程如下所示：
（1）使用copy_from_user从用户空间拷贝fd_set到内核空间
（2）注册回调函数__pollwait
（3）遍历所有fd，调用其对应的poll方法（对于socket，这个poll方法是sock_poll，sock_poll根据情况会调用到...
How to export table as CSV with headings on Postgresql?
...
COPY products_273 TO '/tmp/products_199.csv' WITH (FORMAT CSV, HEADER);
as described in the manual.
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How do I access command line arguments in Python?
...a small example:
import argparse
parser = argparse.ArgumentParser("simple_example")
parser.add_argument("counter", help="An integer will be increased by 1 and printed.", type=int)
args = parser.parse_args()
print(args.counter + 1)
and the output for python prog.py -h
usage: simple_example [-h] ...
List comprehension: Returning two (or more) items for each item
...bda x: x + 2
>>> g = lambda x: x ** 2
>>> list(chain.from_iterable((f(x), g(x)) for x in range(3)))
[2, 0, 3, 1, 4, 4]
Timings:
from timeit import timeit
f = lambda x: x + 2
g = lambda x: x ** 2
def fg(x):
yield f(x)
yield g(x)
print timeit(stmt='list(chain.from_itera...
How to convert ActiveRecord results into an array of hashes
...
as_json
You should use as_json method which converts ActiveRecord objects to Ruby Hashes despite its name
tasks_records = TaskStoreStatus.all
tasks_records = tasks_records.as_json
# You can now add new records and return the...
Python date string to date object
...<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/_strptime.py", line 308, in _strptime
format_regex = _TimeRE_cache.compile(format)
File "/usr/local/lib/python2.7/_strptime.py", line 265, in compile
return re_compile(self.pattern(format), IGNORECASE)
File "/usr/...
clear javascript console in Google Chrome
...
Chrome:
console._commandLineAPI.clear();
Safari:
console._inspectorCommandLineAPI.clear();
You can create your own variable, which works in both:
if (typeof console._commandLineAPI !== 'undefined') {
console.API = console._commandL...
Mathematical functions in Swift
...l math functions and constanst.
A small snippet of the file
...
func pow(_: CDouble, _: CDouble) -> CDouble
func sqrtf(_: CFloat) -> CFloat
func sqrt(_: CDouble) -> CDouble
func erff(_: CFloat) -> CFloat
...
var M_LN10: CDouble { get } /* loge(10) */
var M_PI: CDouble { get } /...
How can we generate getters and setters in Visual Studio?
..., you will have to have an instance variable for it:
private PropertyType _property;
public PropertyType PropertyName
{
get
{
//logic here
return _property;
}
set
{
//logic here
_property = value;
}
}
Previous versions of Visual Studio al...
Calculating arithmetic mean (one type of average) in Python
...
Why have you called max?
– 1 -_-
Jul 25 '17 at 6:41
3
See the question abo...