What can cause a Resource temporarily unavailable on sock send command

Question

What can cause a Resource temporarily unavailable error on a socket send   command  The socket is setup as AF 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

User · Accepted Answer

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 to send    or setting a send timeout with the SO SNDTIMEO socket option

User · Answer

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

User · Answer

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  lt arpa inet h gt   include  lt sys socket h gt   include  lt stdio h gt   include  lt errno h gt   include  lt fcntl h gt   include  lt stdlib h gt   include  lt string h gt   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  lt  0   fcntl failed        int r   fcntl fd  F SETFL  flags   O NONBLOCK       exit if r  lt  0   fcntl failed       void test full sock buf 1        short port   8000      struct sockaddr in addr      memset  amp 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 lt 0   create socket error         int ret   connect fd   struct sockaddr     amp addr  sizeof struct sockaddr        exit if ret lt 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  lt  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  lt arpa inet h gt       include  lt sys socket h gt       include  lt stdio h gt       include  lt errno h gt       include  lt fcntl h gt       include  lt stdlib h gt       include  lt string h gt       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 lt 0   create socket error         short port   8000      struct sockaddr in addr      memset  amp 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     amp addr  sizeof struct sockaddr        exit if r lt 0   bind socket error         r   listen listenfd  100       exit if r lt 0   listen socket error         struct sockaddr in raddr      socklen t rsz   sizeof raddr       int cfd   accept listenfd   struct sockaddr     amp raddr   amp rsz       exit if cfd lt 0   accept socket error         sockaddr in peer      socklen t alen   sizeof peer       getpeername cfd   sockaddr     amp peer   amp 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

[c] What can cause a “Resource temporarily unavailable” on sock send() command

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