Linux Error 4 Interrupted System Call

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Interrupted System Calls In Unix

Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping "interrupted system call" errno 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 My user-space application sometimes blocks after receiving an EINTR-Signal, somehow. What I recorded

Interrupted System Call Select

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_??? */, 2) = ? ERESTARTSYS (To be restarted) --- SIGWINCH (Window changed) @ 0 (0) --- futex(0xb7cea80c, 0x80 error interrupted system call /* 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 1,03531733 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 Answers 2 active oldest votes up vote 15 down vote accepted The code which calls write (or other blocking operations) has to be aware of EINTR. If a signal occurs during a blocking operation, then the operation wi

errno was set to EINTR. This was done under the assumption that since a signal occurred and the process caught it, there is a good chance that something has happened that

Top: Failed Tty Set:

should wake up the blocked system call. Here, we have to differentiate between a

Interrupted System Call (code=4)

system call and a function. It is a system call within the kernel that is interrupted when a signal is caught. poll eintr To support this feature, the system calls are divided into two categories: the "slow" system calls and all the others. The slow system calls are those that can block forever. Included in this category http://stackoverflow.com/questions/1674162/how-to-handle-eintr-interrupted-system-call are Reads that can block the caller forever if data isn't present with certain file types (pipes, terminal devices, and network devices)Writes that can block the caller forever if the data can't be accepted immediately by these same file typesOpens that block until some condition occurs on certain file types (such as an open of a terminal device that waits until an attached modem answers the phone)The pause function (which http://poincare.matf.bg.ac.rs/~ivana/courses/tos/sistemi_knjige/pomocno/apue/APUE/0201433079/ch10lev1sec5.html by definition puts the calling process to sleep until a signal is caught) and the wait functionCertain ioctl operationsSome of the interprocess communication functions (Chapter 15) The notable exception to these slow system calls is anything related to disk I/O. Although a read or a write of a disk file can block the caller temporarily (while the disk driver queues the request and then the request is executed), unless a hardware error occurs, the I/O operation always returns and unblocks the caller quickly. One condition that is handled by interrupted system calls, for example, is when a process initiates a read from a terminal device and the user at the terminal walks away from the terminal for an extended period. In this example, the process could be blocked for hours or days and would remain so unless the system was taken down. POSIX.1 semantics for interrupted reads and writes changed with the 2001 version of the standard. Earlier versions gave implementations a choice for how to deal with reads and writes that have processed partial amounts of data. If read has received and transferred data to an application's buffer, but has not yet received all that the application requested and is then interrupted, the operating system could eith

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 Specification is, and notes that many existing Unix implementations seem to have f*cked this up http://www.madore.org/~david/computers/connect-intr.html somehow. The question is this: if a blocking connect() (on a blocking stream socket, that is) is interrupted by a signal, returning EINTR, in what state is the socket left, and is it permissible to restart http://www.unix.com/programming/98288-problem-signal-handler-interrupted-system-call.html the system call? What happens if a 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 interrupted system 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() 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 interrupted system call 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 connection has been established asynchronously, select() and poll() shall indicate that the file descriptor for the socket is ready for writing. Later on, when listing possible error codes for connect(), the Spec mentions: The connect() function shall fail if: […] [EALREADY] A connection request is already in progress for the specified socket. How does this answer the question above? That is, what is supposed to happen, according to the Spec, when a second connect() is attempted (with the same arguments) just after one which returned EINTR (on a

Java, SQL, and other programming languages here. Search Forums Show Threads Show Posts Tag Search Advanced Search Unanswered Threads Find All Thanked Posts Go to Page... linux operating commands and unix operating commands Problem with signal handler and interrupted system call Programming Thread Tools Search this Thread Display Modes #1 01-26-2009 soeckel Registered User Join Date: Jan 2009 Last Activity: 27 January 2009, 5:07 AM EST Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts Problem with signal handler and interrupted system call Hi, I have a daq program that runs in an infinite loop until it receives SIGINT. A handler catches the signal and sets a flag to stop the while loop. After the loop some things have to be cleaned up. The problem is that I want my main while loop to wait until the next full second begins, to start some action. To do so it waits for the RTC interrupt. Unfortunately the read() which waits for the interrupt seems to be interrupted itself by SIGINT. That causes my program to exit abnormally with Code: read: Interrupted system call and without cleaning up. I already tried it with SIGHUP and SIGUSR1 instead of SIGINT without succes. How could I prevent my read() from being interrupted? Thanks in advance Here are the important code snippets: the loop in main() Code: /* * Signal handling */ struct sigaction act; /* define the signal action */ act.sa_handler = terminate; /* make "act" an empty signal set */ sigemptyset(&act.sa_mask); act.sa_flags = 0; /* instead of SIGHUP do "act" */ sigaction(SIGHUP, &act, 0); /* * main loop : runs until the signal handler * receives a SIGINT to change "keep_running" to 0 */ while(keep_running){ /* wait for irq */ retval = await_rtc_irq(freq); /*.....*/ } syslog (LOG_NOTICE, "clean up and exit\n"); close(fdlock); unlink(DAQD_LOCK_FILE); closelog(); return 0; the wait_for_the_interrupt function Code: long int await_rtc_irq(int freq) { int fd; long int retval, controlval; unsigned long data; /* open the RTC IRQ */ fd = open ("/dev/rtc", O_RDONLY); if (freq == 1) { /* Enable periodic 1Hz interrupts */ retval = ioctl(fd, RTC_UIE_ON, 0); if (retval == -1) { perror("ioctl"); exit(errno); } /* call the read function to await the Alarm interrupt */ retval = read(fd, &data, sizeof(unsigned long)); if (retval == -1) { perror("read"); exit(errno); } controlval = retval; /* Turn off update interrupts */ retval = ioctl(fd, RTC_UIE_OFF, 0); if (retval == -1) { perror("RTC_UIE_OFF ioctl"); exit(errno); } } /* For frequencies different from 1 the irq has to be set different