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求教网络多次connect的问题?

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Jun 06, 2016 pm 08:06 PM

httpipphptcp

在查看有时候文件上传到cdn比较慢的情况。
使用strace查看到以下系统调用。
求教网络多次connect的问题?

我有一些疑问：

查询dns的时候，connect了一次之后，为何会有两次sendto。看样子两次都发送了同个域名过去。
连接cdn的时候出现了多次connect，我很不理解这个过程，可否帮我讲解下，发生了什么，为什么这样。

<code>futex(0x7fbfc9b9ff04, FUTEX_WAKE_PRIVATE, 2147483647) = 0
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 6
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("221.181.196.155")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(44696), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
connect(6, {sa_family=AF_UNSPEC, sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16) = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("211.142.193.60")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(45965), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
connect(6, {sa_family=AF_UNSPEC, sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16) = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("183.203.25.158")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(59516), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
close(6)                                = 0
gettimeofday({1464771775, 191396}, NULL) = 0
alarm(0)                                = 30
rt_sigaction(SIGALRM, {SIG_DFL, [], SA_RESTORER, 0x7fbfc98419a0}, NULL, 8) = 0
clock_gettime(CLOCK_MONOTONIC, {11494888, 559945294}) = 0
clock_gettime(CLOCK_MONOTONIC, {11494888, 560020269}) = 0
socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 6
fcntl(6, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("221.181.196.155")}, 16) = -1 EINPROGRESS (Operation now in progress)</code>

回复内容：

在查看有时候文件上传到cdn比较慢的情况。
使用strace查看到以下系统调用。
求教网络多次connect的问题?

我有一些疑问：

查询dns的时候，connect了一次之后，为何会有两次sendto。看样子两次都发送了同个域名过去。
连接cdn的时候出现了多次connect，我很不理解这个过程，可否帮我讲解下，发生了什么，为什么这样。

<code>futex(0x7fbfc9b9ff04, FUTEX_WAKE_PRIVATE, 2147483647) = 0
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 6
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("221.181.196.155")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(44696), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
connect(6, {sa_family=AF_UNSPEC, sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16) = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("211.142.193.60")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(45965), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
connect(6, {sa_family=AF_UNSPEC, sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16) = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("183.203.25.158")}, 16) = 0
getsockname(6, {sa_family=AF_INET, sin_port=htons(59516), sin_addr=inet_addr("10.250.1.110")}, [16]) = 0
close(6)                                = 0
gettimeofday({1464771775, 191396}, NULL) = 0
alarm(0)                                = 30
rt_sigaction(SIGALRM, {SIG_DFL, [], SA_RESTORER, 0x7fbfc98419a0}, NULL, 8) = 0
clock_gettime(CLOCK_MONOTONIC, {11494888, 559945294}) = 0
clock_gettime(CLOCK_MONOTONIC, {11494888, 560020269}) = 0
socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 6
fcntl(6, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
connect(6, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("221.181.196.155")}, 16) = -1 EINPROGRESS (Operation now in progress)</code>

tcp 三次握手

cdn 会连接到多个节点

第一个问题我不知道。

第二个，解析DNS之后会有多个A记录，看样子先进行了测速之类的任务，然后选择最优服务器上传数据。

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