What can cause a “Resource temporarily unavailable” on sock send() command
Solution 1
"Resource temporarily unavailable"
is the error message corresponding to EAGAIN
, which means that the operation would have blocked but nonblocking operation was requested. For send()
, that could be due to any of:
- explicitly marking the file descriptor as nonblocking with
fcntl()
; or - passing the
MSG_DONTWAIT
flag tosend()
; or - setting a send timeout with the
SO_SNDTIMEO
socket option.
Solution 2
That's because you're using a non-blocking
socket and the output buffer is full.
From the send()
man page
When the message does not fit into the send buffer of the socket,
send() normally blocks, unless the socket has been placed in non-block-
ing I/O mode. In non-blocking mode it would return EAGAIN in this
case.
EAGAIN is the error code tied to "Resource temporarily unavailable"
Consider using select()
to get a better control of this behaviours
Solution 3
Let'e me give an example:
client connect to server, and send 1MB data to server every 1 second.
server side accept a connection, and then sleep 20 second, without recv msg from client.So the
tcp send buffer
in the client side will be full.
Code in client side:
#include <arpa/inet.h>
#include <sys/socket.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#define exit_if(r, ...) \
if (r) { \
printf(__VA_ARGS__); \
printf("%s:%d error no: %d error msg %s\n", __FILE__, __LINE__, errno, strerror(errno)); \
exit(1); \
}
void setNonBlock(int fd) {
int flags = fcntl(fd, F_GETFL, 0);
exit_if(flags < 0, "fcntl failed");
int r = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
exit_if(r < 0, "fcntl failed");
}
void test_full_sock_buf_1(){
short port = 8000;
struct sockaddr_in addr;
memset(&addr, 0, sizeof addr);
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = INADDR_ANY;
int fd = socket(AF_INET, SOCK_STREAM, 0);
exit_if(fd<0, "create socket error");
int ret = connect(fd, (struct sockaddr *) &addr, sizeof(struct sockaddr));
exit_if(ret<0, "connect to server error");
setNonBlock(fd);
printf("connect to server success");
const int LEN = 1024 * 1000;
char msg[LEN]; // 1MB data
memset(msg, 'a', LEN);
for (int i = 0; i < 1000; ++i) {
int len = send(fd, msg, LEN, 0);
printf("send: %d, erron: %d, %s \n", len, errno, strerror(errno));
sleep(1);
}
}
int main(){
test_full_sock_buf_1();
return 0;
}
Code in server side:
#include <arpa/inet.h>
#include <sys/socket.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#define exit_if(r, ...) \
if (r) { \
printf(__VA_ARGS__); \
printf("%s:%d error no: %d error msg %s\n", __FILE__, __LINE__, errno, strerror(errno)); \
exit(1); \
}
void test_full_sock_buf_1(){
int listenfd = socket(AF_INET, SOCK_STREAM, 0);
exit_if(listenfd<0, "create socket error");
short port = 8000;
struct sockaddr_in addr;
memset(&addr, 0, sizeof addr);
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = INADDR_ANY;
int r = ::bind(listenfd, (struct sockaddr *) &addr, sizeof(struct sockaddr));
exit_if(r<0, "bind socket error");
r = listen(listenfd, 100);
exit_if(r<0, "listen socket error");
struct sockaddr_in raddr;
socklen_t rsz = sizeof(raddr);
int cfd = accept(listenfd, (struct sockaddr *) &raddr, &rsz);
exit_if(cfd<0, "accept socket error");
sockaddr_in peer;
socklen_t alen = sizeof(peer);
getpeername(cfd, (sockaddr *) &peer, &alen);
printf("accept a connection from %s:%d\n", inet_ntoa(peer.sin_addr), ntohs(peer.sin_port));
printf("but now I will sleep 15 second, then exit");
sleep(15);
}
Start server side, then start client side.
server side may output:
accept a connection from 127.0.0.1:35764
but now I will sleep 15 second, then exit
Process finished with exit code 0
client side may output:
connect to server successsend: 1024000, erron: 0, Success
send: 1024000, erron: 0, Success
send: 1024000, erron: 0, Success
send: 552190, erron: 0, Success
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 11, Resource temporarily unavailable
send: -1, erron: 104, Connection reset by peer
send: -1, erron: 32, Broken pipe
send: -1, erron: 32, Broken pipe
send: -1, erron: 32, Broken pipe
send: -1, erron: 32, Broken pipe
send: -1, erron: 32, Broken pipe
You can see, as the server side doesn't recv the data from client, so when the client side tcp buffer
get full, but you still send data, so you may get Resource temporarily unavailable
error.
Comments
-
giroy about 4 years
What can cause a
Resource temporarily unavailable
error on a socketsend()
command? The socket is setup asAF_UNIX, SOCK_STREAM
. It works most of the time, but occasionally gets this error. The receiving end of the socket appears to be working properly.I know this isn't very detailed, but I'm just looking for general ideas. Thanks!
-
giroy over 11 yearsThe cause of my problem was setting the send timeout. Thank you for you help!
-
Codename_DJ over 7 years@caf, In my case, different MTU size configuration in two side was causing sctp association Txqueue to be overflown when high rate of packet exchange was happening. Making the MTU same on both system made the problem go away. But can anyone please explain what is the reason behind the problem?
-
EML almost 6 years@giroy: but not actually right... actually a blocking socket, with
SO_SNDTIMEO
-
MUY Belgium over 4 yearsCool but how can we use other connection to manage simultaneous read in the DB?
-
Gabriel Fernandez about 3 yearsWhy does setting SO_SNDTIMEO cause the error to happen? How to use that flag correctly?
-
caf about 3 years@GabrielFernandez: Because this is what
SO_SNDTIMEO
requests: that the send not block for longer than the timeout period. If the send hasn't completed and the timeout expires, it returnsEAGAIN
to indicate this condition. How you handle that is up to your application, bearing in mind that the data you tried to send has not been sent.