gethostbyname crée un fil?
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24-10-2019 - |
Question
Je travaille en C ++ avec VS2008 et Win7.
Lors de l'examen d'un programme que je suivais les fils créés, et il semble que gethostbyname () crée un fil pour lui-même. Pourriez-vous expliquer pourquoi?
Le msdn est dit: « La mémoire de la structure hostent retournée par la fonction gethostbyname est alloué en interne par la DLL Winsock de stockage local des threads. »
Est-ce que ce fou mémoire visual studio en pensant que c'est un fil?
EDIT: Il semble que de ce lien , et aussi de mes observations que cela se produit aussi avec la fonction Connect. Je suppose que ce comportement est normal.
Le code ci-dessous est de msdn [page gethostbyname] et il présente le même comportement.
int main(int argc, char **argv)
{
//-----------------------------------------
// Declare and initialize variables
WSADATA wsaData;
int iResult;
DWORD dwError;
int i = 0;
struct hostent *remoteHost;
char *host_name;
struct in_addr addr;
char **pAlias;
// Validate the parameters
if (argc != 2) {
printf("usage: %s hostname\n", argv[0]);
printf(" to return the IP addresses for the host\n");
printf(" %s www.contoso.com\n", argv[0]);
printf(" or\n");
printf(" %s IPv4string\n", argv[0]);
printf(" to return an IPv4 binary address for an IPv4string\n");
printf(" %s 127.0.0.1\n", argv[0]);
return 1;
}
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed: %d\n", iResult);
return 1;
}
host_name = argv[1];
printf("Calling gethostbyname with %s\n", host_name);
remoteHost = gethostbyname(host_name);
if (remoteHost == NULL) {
dwError = WSAGetLastError();
if (dwError != 0) {
if (dwError == WSAHOST_NOT_FOUND) {
printf("Host not found\n");
return 1;
} else if (dwError == WSANO_DATA) {
printf("No data record found\n");
return 1;
} else {
printf("Function failed with error: %ld\n", dwError);
return 1;
}
}
} else {
printf("Function returned:\n");
printf("\tOfficial name: %s\n", remoteHost->h_name);
for (pAlias = remoteHost->h_aliases; *pAlias != 0; pAlias++) {
printf("\tAlternate name #%d: %s\n", ++i, *pAlias);
}
printf("\tAddress type: ");
switch (remoteHost->h_addrtype) {
case AF_INET:
printf("AF_INET\n");
break;
case AF_NETBIOS:
printf("AF_NETBIOS\n");
break;
default:
printf(" %d\n", remoteHost->h_addrtype);
break;
}
printf("\tAddress length: %d\n", remoteHost->h_length);
i = 0;
if (remoteHost->h_addrtype == AF_INET)
{
while (remoteHost->h_addr_list[i] != 0) {
addr.s_addr = *(u_long *) remoteHost->h_addr_list[i++];
printf("\tIP Address #%d: %s\n", i, inet_ntoa(addr));
}
}
else if (remoteHost->h_addrtype == AF_NETBIOS)
{
printf("NETBIOS address was returned\n");
}
}
return 0;
}
La solution
AFAIK, gethostbyname blocks.
WinSock often creates some helper threads though.
Autres conseils
No, the Thread-local storage is unrelated to the startup of a new thread.
The thread may be needed due to thread-affinity issues with sub-operations of the GetHostByName API, such as the need to use asynchronous callbacks without affecting the calling thread's re-entrancy.
Or it may be a lazy initialization feature of WinSock where a daemon thread needed for a subset of WinSock operations is needed, and this was the first API to require the daemon.