Accept Error Interrupted System Call
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Waitpid Error Interrupted System Call
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Interrupted System Call @ Rb_sysopen
up TCP sockets, server fails to respond to client, accept: Interrupted system call up vote 0 down vote favorite I am trying to implement a TCP server and client in C, running on Solaris. I am new to sockets and am using Beej's Guide as an example. For starters, what I would like is for the client to send a message to the
Interrupted System Call Linux
server in the form of word1 word2. Upon receipt, I want the server to extract word2 from the message and send that back to the client. The initial client --> server message sending works fine. But the server --> client response is not working. There are several failure symptoms: The server does not appear to even try to send() anything to the client. After receiving the client's message, the server prints: accept: Interrupted system call, then returns to the top of the while(1) loop and remains there until I Ctrl-C out of it. The client's call to recv() returns 0 bytes. I found an old thread here, where the last post says this: accept is being interrupted by the child process sending a signal back to the parent when it terminates (SIGCHLD, if I remember write). You can either ignore SIGCHLD, or you can code accept() to handle the interrupt better (errno is set to EINTR) However, I'm not understanding this. Why is the child process terminating before even attempting the send() portion? What does "handle the interrupt better" mean? After searching some more, I found this
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Interrupted System Call Fastcgi Comm With Server
us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is interrupted system call (code=4) a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up How to handle EINTR (interrupted System Call) up vote 3 down vote favorite 3 http://stackoverflow.com/questions/20067657/tcp-sockets-server-fails-to-respond-to-client-accept-interrupted-system-call My user-space application sometimes blocks after receiving an EINTR-Signal, somehow. What I recorded with strace: time(NULL) = 1257343042 time(NULL) = 1257343042 rt_sigreturn(0xbff07be4) = -1 EINTR (Interrupted system call) --- SIGALRM (Alarm clock) @ 0 (0) --- time(NULL) = 1257343042 futex(0xb7cea80c, 0x80 /* FUTEX_??? */, 2) = ? ERESTARTSYS (To be restarted) --- SIGUSR1 (User defined signal 1) @ 0 (0) --- sigreturn() = ? (mask now [ALRM]) futex(0xb7cea80c, 0x80 /* FUTEX_??? http://stackoverflow.com/questions/1674162/how-to-handle-eintr-interrupted-system-call */, 2) = ? ERESTARTSYS (To be restarted) --- SIGWINCH (Window changed) @ 0 (0) --- futex(0xb7cea80c, 0x80 /* FUTEX_??? */, 2) = ? ERESTARTSYS (To be restarted) --- SIGTERM (Terminated) @ 0 (0) --- time(NULL) = 1257343443 time(NULL) = 1257343443 futex(0xb7cea80c, 0x80 /* FUTEX_??? */, 2) = ? ERESTARTSYS (To be restarted) --- SIGWINCH (Window changed) @ 0 (0) --- futex(0xb7cea80c, 0x80 /* FUTEX_??? */, 2 Can I catch the EINTR signal and how can I repeat concerned calls such as write, read or select? How can I determine WHERE this EINTR occurred, even if I used third-party libraries working with system calls? Why my app is completely blocked after receiving an EINTR (see strace dump: I sent a SIGUSR1 which normally should be handled)? And why is futex() returning ERESTARTSYS to user space? thanks c++ c linux share|improve this question asked Nov 4 '09 at 14:40 Maus 1,01531733 3 EINTR is not a signal but an error number returned upon a system call interrupted by a signal. –Nikolai N Fetissov Nov 4 '09 at 15:06 Use gstack or gdb to get a stack trace, to find out where the program is currently stuck. –mark4o Nov 4 '09 at 16:08 add a comment| 2 Answer
point about the behavior of the Unix (socket API) connect() system call when it is interrupted by a signal. It points out how obscure the Single Unix http://www.madore.org/~david/computers/connect-intr.html Specification is, and notes that many existing Unix implementations seem to have f*cked this up somehow. The question is this: if a blocking connect() (on a blocking stream socket, http://unix.stackexchange.com/questions/16455/interruption-of-system-calls-when-a-signal-is-caught that is) is interrupted by a signal, returning EINTR, in what state is the socket left, and is it permissible to restart the system call? What happens if a interrupted system second connect() with the same arguments is attempted immediately after one failed with EINTR? The reference for connect() (hereafter, “the Spec”) is part of the Open Group's Single Unix Specification, version3 (note: you may need to register to read this; see also here). Here is the relevant part of it: If the initiating socket is connection-mode, then connect() interrupted system call shall attempt to establish a connection to the address specified by the address argument. If the connection cannot be established immediately and O_NONBLOCK is not set for the file descriptor for the socket, connect() shall block for up to an unspecified timeout interval until the connection is established. If the timeout interval expires before the connection is established, connect() shall fail and the connection attempt shall be aborted. If connect() is interrupted by a signal that is caught while blocked waiting to establish a connection, connect() shall fail and set connect() to [EINTR], but the connection request shall not be aborted, and the connection shall be established asynchronously. If the connection cannot be established immediately and O_NONBLOCK is set for the file descriptor for the socket, connect() shall fail and set errno to [EINPROGRESS], but the connection request shall not be aborted, and the connection shall be established asynchronously. Subsequent calls to connect() for the same socket, before the connection is established, shall fail and set errno to [EALREADY]. When the c
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Unix & Linux Questions Tags Users Badges Unanswered Ask Question _ Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top Interruption of system calls when a signal is caught up vote 18 down vote favorite 4 From reading the man pages on the read() and write() calls it appears that these calls get interrupted by signals regardless of whether they have to block or not. In particular, assume a process establishes a handler for some signal. a device is opened (say, a terminal) with the O_NONBLOCK not set (i.e. operating in blocking mode) the process then makes a read() system call to read from the device and as a result executes a kernel control path in kernel-space. while the precess is executing its read() in kernel-space, the signal for which the handler was installed earlier is delivered to that process and its signal handler is invoked. Reading the man pages and the appropriate sections in SUSv3 'System Interfaces volume (XSH)', one finds that: i. If a read() is interrupted by a signal before it reads any data (i.e. it had to block because no data was available), it returns -1 with errno set to [EINTR]. ii. If a read() is interrupted by a signal after it has successfully read some data (i.e. it was possible to start servicing the request immediately), it returns the number of bytes read. Question A): Am I correct to assume that in either case (block/no block) the delivery and handling of the signal is not entirely transparent to the read()? Case i. seems understandable since the blocking read() would normally place the process in the TASK_INTERRUPTIBLE state so that when a signal is delivered, the kernel places the process into TASK_RUNNING state. However when the read() doesn't need to block (case ii.) and is processing the request in kernel-space, I would have thought that the arrival of a signal and its handling would be transparent much like the arrival and proper handling of a HW interrupt would