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How efficient is locking an unlocked mutex? What is the cost of a mutex?
... it causes to much of the inter-CPU/core traffic to flush the mutex memory from the data cache of other CPUs to guarantee the cache coherency. The cache flushes are like light-weight interrupts and handled by CPUs transparently - but they do introduce so called stalls (search for "stall").
And the ...
What is the most effective way for float and double comparison?
...hen looking at floating point comparison.
The following definitions are from The art of computer programming by Knuth:
bool approximatelyEqual(float a, float b, float epsilon)
{
return fabs(a - b) <= ( (fabs(a) < fabs(b) ? fabs(b) : fabs(a)) * epsilon);
}
bool essentiallyEqual(float ...
#define macro for debug printing in C?
...ebugging. Several times, having the printing always validated has saved me from later problems.
I use NDEBUG to control assertions only, and a separate macro (usually DEBUG) to control whether debug tracing is built into the program. Even when the debug tracing is built in, I frequently do not want...
Awk学习笔记 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...列中以root开头的行。
10. 比较表达式
conditional expression1 ? expression2: expression3，例如：$ awk '{max = {$1 > $3} ? $1: $3: print max}' test。如果第一个域大于第三个域，$1就赋值给max，否则$3就赋值给max。
$ awk '$1 + $2 < 100' test。如果...
What's so bad about Template Haskell?
...e wrong, I don't see TH as being that complicated of a compiler extension, from an implementation perspective. This is actually one of the benefits of "keeping it simple" and not having the fundamental layer be some theoretically appealing, statically verifiable templating system.
The API is...
How does Google Instant work?
...ive. The search results are from the first autocomplete suggestion (or the selected one if you hit the down arrow or mouse over a suggestion).
In other words if I type "vinyl s", the first autocomplete suggestion is "vinyl siding," and the search results clearly show a search for "vinyl siding." If...
LINGO使用指南 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...它可以用于剪贴板中的内容不是文本的情形。
6． 全选(Select All)
从编辑菜单中选用“Select All”命令或按Ctrl+A组合键可选定当前窗口中的所有内容。
7． 匹配小括号(Match Parenthesis)
从编辑菜单中选用“Match Parenthesis”命令...
generate days from date range
...000 days, and could be extended to go as far back or forward as you wish.
select a.Date
from (
select curdate() - INTERVAL (a.a + (10 * b.a) + (100 * c.a) + (1000 * d.a) ) DAY as Date
from (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all ...
Efficiently convert rows to columns in sql server
...ou can use the PIVOT function to transform the data from rows to columns:
select Firstname, Amount, PostalCode, LastName, AccountNumber
from
(
select value, columnname
from yourtable
) d
pivot
(
max(value)
for columnname in (Firstname, Amount, PostalCode, LastName, AccountNumber)
) piv;
S...
Is it possible to use the SELECT INTO clause with UNION [ALL]?
...
This works in SQL Server:
SELECT * INTO tmpFerdeen FROM (
SELECT top 100 *
FROM Customers
UNION All
SELECT top 100 *
FROM CustomerEurope
UNION All
SELECT top 100 *
FROM CustomerAsia
UNION All
SELECT top 100 *
FROM CustomerAme...