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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...
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...
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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improve this answer
...
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] ...
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/...
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 } /...
What is the correct way to create a single-instance WPF application?
... NativeMethods.PostMessage(
(IntPtr)NativeMethods.HWND_BROADCAST,
NativeMethods.WM_SHOWME,
IntPtr.Zero,
IntPtr.Zero);
}
}
}
NativeMethods.cs
// this class just wraps some Win32 stuff that we're going to use...
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...
Read properties file outside JAR file
...main properties file is main.properties):
./ - the root of your program
|__ main.jar
|__ main.properties
With this architecture, you can modify any property in the main.properties file using any text editor before or while your main.jar is running (depending on the current state of the program)...