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Full Discussion: read/write socket error
Top Forums Programming read/write socket error Post 302113706 by gio on Monday 9th of April 2007 09:31:31 AM
Old 04-09-2007
read/write socket error
I have client and server connected.
client write and read from csock.
server write and read from ssock
suppose the server does :
....
close(ssock); //send FIN to client
othertask();
....

READ ERROR


if after the server close() the client does:
...
read(csock,...);
...
read(csock,...);
...
close(csock,...);
...
read(csock,...);
...


first read return 0 (read FIN)


second read also return 0.


third read return -1 with errno set to EBADF.


QUESTION 1:
Indeed if after the server close() the client does:
....
write(csock, "hello", 6); //server send RST
...
read(csock,...);
...
write(csock, ...);


first write return 6 without signaling nothing.


read return:
0 if the client read before the RST arrives.
-1 with errno set to ECONNRESET otherwise.


second write comports the SIGPIPE signal.
if it is ignored write return -1 and errno=EPIPE, otherwise it
comports the client termination.
is ok?


IS THE SITUATION THE SAME WHEN THE SERVER CRASH BEFORE THE CLIENT'S
FIRST WRITE?


QUESTION 2:
when read fails with errno=ENOTCONN?


QUESTION 3:
In general if I don't set the timeout option, is possible that a
read() fails with errno=ETIMEDOUT?


WRITE ERROR


when write fails and errno =ECONNRESET??
 

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LEARN ABOUT OSF1

nfsiod

nfsiod(8)						      System Manager's Manual							 nfsiod(8)

NAME

       nfsiod, biod - The local NFS compatible asynchronous I/O daemon

SYNOPSIS

       nfsiod [ numthreads ]

DESCRIPTION

       The  nfsiod  daemon  runs  on  an  NFS  compatible client machine and spawns several IO threads to service asynchronous I/O requests to its
       server.	The I/O threads improve performance of both NFS reads and writes. Both try to enlist the aid of an idle I/O thread.   If  none	is
       available, the process itself issues the request to the server and waits for the reply.

       The  optimum number of I/O threads to run depends on many variables, such as how quickly the client will be writing, how many files will be
       accessed simultaneously, and the behaviour of the NFS server. For use with a Tru64 UNIX server, 7 is a good number of I/O threads for  most
       systems.

       When  reading,  if  the client believes the process is reading a file sequentially, it requests an I/O thread to read a block ahead of what
       the process is currently requesting.  If the readahead completes before the process asks for that block, then the  subsequent  read  system
       call  for that data completes immediately and does not have to wait for the NFS request to complete.  Read ahead will be triggered again so
       the read may find that next block available as well.

       When writing a file, the client takes the process's data, passes the request to an I/O thread and immediately returns to the  process.	If
       the  process is writing data faster than the network or server can process, then eventually all the I/O threads become busy and the process
       has to handle a NFS write itself.  This means the process has to wait until the server finishes the write.  For Tru64 UNIX servers, the NFS
       block  size  is	8Kb and UFS tries to cluster I/O 64Kbs at a time.  If the client is running with 7 I/O threads, 8 write requests can be in
       progress at once.  This allows the client and server to write data 64Kbs at a time and is the reason for recommending 7 I/O threads.

       Unlike nfsd, each client thread can use either UDP or TCP.  However, if TCP mounts are active, the nfsiod process will time out, close idle
       TCP connections, and acknowledge any connections closed by the server.

       The nfsiod process is also responsible for syncing the access time and modify times for special files and named pipes (fifos).  Because I/O
       to these files does not go through the NFS server, NFS clients have to directly update the access time and modify time attributes.

       The client threads are implemented as kernel threads; they are part of Process ID 0, not the nfsiod process.  The ps axml command  displays
       idle  I/O  threads  under  PID  0.  Idle threads will be waiting on nfsiod_wait.  Therefore, if 7 I/O threads are configured, only 1 nfsiod
       process is displayed in the output from the ps command, although 7 client threads are available to handle NFS requests.

FILES

       Specifies the command path Specifies the file for logging NFS activity.

RELATED INFORMATION

       Commands: nfsd(8), nfsstat(8)

       Daemons: async_daemon(2) delim off

																	 nfsiod(8)
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