To understand the backlog argument, we must realize that for a given listening socket, the kernel maintains two queues :
要明白backlog參數(shù)的含義，我們必須明白對(duì)于一個(gè)listening socket，kernel維護(hù)者兩個(gè)隊(duì)列：
1.An incomplete connection queue, which contains an entry for each SYN that has arrived from a client for which the server is awaiting completion of the TCP three-way handshake. These sockets are in the SYN_RCVD state .
1.一個(gè)未完成連接的隊(duì)列，此隊(duì)列維護(hù)著那些已收到了客戶(hù)端SYN分節(jié)信息，等待完成三路握手的連接，socket的狀態(tài)是SYN_RCVD
2.A completed connection queue, which contains an entry for each client with whom the TCP three-way handshake has completed. These sockets are in the ESTABLISHED state
2.一個(gè)已完成的連接的隊(duì)列，此隊(duì)列包含了那些已經(jīng)完成三路握手的連接，socket的狀態(tài)是ESTABLISHED
The backlog argument to the listen function has historically specified the maximum value for the sum of both queues.
backlog參數(shù)歷史上被定義為上面兩個(gè)隊(duì)列的大小之和
Berkeley-derived implementations add a fudge factor to the backlog: It is multiplied by 1.5
Berkely實(shí)現(xiàn)中的backlog值為上面兩隊(duì)列之和再乘以1.5
When a SYN arrives from a client, TCP creates a new entry on the incomplete queue and then responds with the second segment of the three-way handshake: the server's SYN with an ACK of the client's SYN (Section 2.6). This entry will remain on the incomplete queue until the third segment of the three-way handshake arrives (the client's ACK of the server's SYN), or until the entry times out. (Berkeley-derived implementations have a timeout of 75 seconds for these incomplete entries.)
當(dāng)客戶(hù)端的第一個(gè)SYN到達(dá)的時(shí)候，TCP會(huì)在未完成隊(duì)列中增加一個(gè)新的記錄然后回復(fù)給客戶(hù)端三路握手中的第二個(gè)分節(jié)(服務(wù)端的SYN和針對(duì)客戶(hù)端的ACK)，這條記錄會(huì)在未完成隊(duì)列中一直存在，直到三路握手中的最后一個(gè)分節(jié)到達(dá)，或者直到超時(shí)(Berkeley時(shí)間將這個(gè)超時(shí)定義為75秒)
If the queues are full when a client SYN arrives, TCP ignores the arriving SYN (pp. 930–931 of TCPv2); it does not send an RST. This is because the condition is considered temporary, and the client TCP will retransmit its SYN, hopefully finding room on the queue in the near future. If the server TCP immediately responded with an RST, the client's connect would return an error, forcing the application to handle this condition instead of letting TCP's normal retransmission take over. Also, the client could not differentiate between an RST in response to a SYN meaning "there is no server at this port" versus "there is a server at this port but its queues are full."
如果當(dāng)客戶(hù)端SYN到達(dá)的時(shí)候隊(duì)列已滿，TCP將會(huì)忽略后續(xù)到達(dá)的SYN，但是不會(huì)給客戶(hù)端發(fā)送RST信息，因?yàn)榇藭r(shí)允許客戶(hù)端重傳SYN分節(jié)，如果返回錯(cuò)誤信息，那么客戶(hù)端將無(wú)法分清到底是服務(wù)端對(duì)應(yīng)端口上沒(méi)有相應(yīng)應(yīng)用程序還是服務(wù)端對(duì)應(yīng)端口上隊(duì)列已滿這兩種情況
今天看到有人在問(wèn)這個(gè)問(wèn)題，寫(xiě)了下代碼，標(biāo)準(zhǔn)庫(kù)分離了算法和數(shù)據(jù)結(jié)構(gòu)，按照這個(gè)框架寫(xiě)程序確實(shí)比較方便，個(gè)人認(rèn)為熟讀和透徹理解標(biāo)準(zhǔn)庫(kù)源碼是每個(gè)想成為資深c++程序員的必修課，就框架結(jié)構(gòu)而論，stl很好的分離了算法和數(shù)據(jù)結(jié)構(gòu)，就算法而論，標(biāo)準(zhǔn)庫(kù)里有很多常見(jiàn)算法的經(jīng)典實(shí)現(xiàn)，所以有非常高的研究?jī)r(jià)值。
#include <iostream>
#include <stddef.h>
#include <stdlib.h>
#include <string>
#include <iterator>
#include <algorithm>
#include <vector>
using namespace std;
template <typename InputIterator1, typename InputIterator2, typename OutputIterator>
OutputIterator delete_intersection(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2, OutputIterator dest)
{
while (first1 != last1 && first2 != last2) {
if (*first1 > *first2) {
*dest = *first2;
++first2;
++dest;
} else if (*first1 < *first2) {
*dest = *first1;
++first1;
++dest;
} else {
++first1;
++first2;
}
}
for (;first2 != last2; ++first2) *dest = *first2;
return dest;
}
int main() {
int a[] = {1,1,2,2,5,6,9,9};
int b[] = {1,2,3,4,4,6,7,8,9,9,9,10};
vector<int> vc;
delete_intersection(a, a + sizeof(a)/sizeof(a[0]), b, b + sizeof(b)/sizeof(b[0]), back_inserter(vc));
std::copy(a, a + sizeof(a)/sizeof(a[0]), ostream_iterator<int>(cout, ","));
cout << endl;
std::copy(b, b + sizeof(b)/sizeof(b[0]), ostream_iterator<int>(cout, ","));
cout << endl;
std::copy(vc.begin(), vc.end(), ostream_iterator<int>(cout, ","));
cout << endl;
::system("PAUSE");
return EXIT_SUCCESS;
}
boost的線程庫(kù)不能強(qiáng)行終止，所以通過(guò)time_wait可以讓其自然的結(jié)束
1 #include <iostream>
2 #include <boost/thread/thread.hpp>
3 #include <boost/thread/mutex.hpp>
4 #include <boost/thread/condition.hpp>
5 #include <boost/date_time/posix_time/posix_time.hpp>
6
7 using namespace std;
8 using namespace boost;
9
10 boost::mutex test_mutex;
11 boost::condition_variable test_condition;
12
13 void test() {
14
15 for (;;) {
16
17 boost::mutex::scoped_lock lock(test_mutex);
18 if (test_condition.timed_wait(lock, get_system_time() + posix_time::seconds(3))) {
19 cout << "成功接收到通知" << endl; //這里加個(gè)break就結(jié)束了
20 } else {
21 cout << "沒(méi)有等待到通知" << endl;
22 }
23
24 }
25 }
26
27 int main() {
28
29 boost::thread test_thread(test);
30
31 for (;;) {
32 ::system("PAUSE");
33 cout << "開(kāi)始發(fā)送通知" << endl;
34 test_condition.notify_one();
35 }
36
37 }
在泛型編程中，對(duì)于一個(gè)concept的一系列modeling，尤其是這些modeling中還有c++基本類(lèi)型的時(shí)候，如果要抽取其特性，可以用一個(gè)traits類(lèi)來(lái)解決，traits的名稱(chēng)可命名為concept名稱(chēng)_traits，對(duì)于其中的基本類(lèi)型的traits可以用類(lèi)模板的偏特化實(shí)現(xiàn)。
程序中幾個(gè)線程一起往控制臺(tái)寫(xiě)入log_info，但是可以很清楚的看到begin or write_process不會(huì)同時(shí)連續(xù)的出現(xiàn)，而且在begin of write_process和end of write_process之間肯定不會(huì)出現(xiàn)begin of read_process或者end of read_process。但是begin of read_process卻會(huì)在控制臺(tái)上連續(xù)出現(xiàn)，這說(shuō)明在同一時(shí)刻只有一個(gè)write_prcess在運(yùn)行，但是wrte_process沒(méi)有運(yùn)行的時(shí)候，會(huì)有多個(gè)read_process并發(fā)運(yùn)行。
1 #include <iostream>
2
3 #include <boost/thread/thread.hpp>
4 #include <boost/thread/shared_mutex.hpp>
5
6 using namespace std;
7 using namespace boost;
8
9 boost::shared_mutex shr_mutex;
10
11 /// 這個(gè)是輔助類(lèi)，能夠保證log_info被完整的輸出
12 class safe_log {
13 public:
14 static void log(const std::string& log_info) {
15 boost::mutex::scoped_lock lock(log_mutex);
16 cout << log_info << endl;
17 }
18
19 private:
20 static boost::mutex log_mutex;
21 };
22
23 boost::mutex safe_log::log_mutex;
24
25 void write_process() {
26 shr_mutex.lock();
27 safe_log::log("begin of write_process");
28 safe_log::log("end of write_process");
29 shr_mutex.unlock();
30 }
31
32 void read_process() {
33 shr_mutex.lock_shared();
34 safe_log::log("begin of read_process");
35 safe_log::log("end of read_process");
36 shr_mutex.unlock_shared();
37 }
38
39 int main() {
40
41 thread_group threads;
42 for (int i = 0; i < 10; ++ i) {
43 threads.create_thread(&write_process);
44 threads.create_thread(&read_process);
45 }
46
47 threads.join_all();
48
49 ::system("PAUSE");
50
51 return 0;
52 }
1、安裝stlport，參考文章：http://www.cnblogs.com/DonLiang/archive/2007/10/13/923143.html
如果是DEBUG模式請(qǐng)?jiān)陧?xiàng)目的屬性=>配置屬性=>c/c++=>命令行的附加選項(xiàng)增加/D_STLP_DEBUG
2、boost_1_37_0\tools\jam\stage下運(yùn)行build.bat編譯生成bjam.exe并拷貝到boost根目錄
3、修改配置文件boost_1_37_0\tools\build\v2\user-config.jam，將兩個(gè)stlport選項(xiàng)打開(kāi)
4、vs2005命令提示下編譯命令：bjam stdlib=stlport --build-type=complete install，接下來(lái)是漫長(zhǎng)的等待，大概兩個(gè)小時(shí)以上吧