Usually when a program is run from the Windows console, the console will wait for the process to exit and then print the prompt and wait for user input. However, if the process starts a child process, the console will still only wait for the first process to exit. It will not wait for the child as well.
Is there a way for the program to get the console to wait on another child process instead of (or as well as) the current process.
I would assume it's impossible because presumably the console is waiting on the process' handle and there's no way to replace that handle. However, I'm struggling to find any confirmation of this.
Is there a way for the program to get the console to wait on another child process instead of (or as well as) the current process.
No. As you noted, as soon as the 1st process the console creates has exited, the console stops waiting. It has no concept of any child processes being created by that 1st process.
So, what you can do instead is either:
simply have the 1st process wait for any child process it creates before then exiting itself.
if that is not an option, then create a separate helper process that creates a Job Object and then starts the main process and assigns it to that job. Any child processes it creates will automatically be put into the same job as well 1. The helper process can then wait for all processes in the job to exit before then exiting itself. Then, you can have the console run and wait on the helper process rather than the main process.
1: by default - a process spawner can choose to break out a new child process from the current job, if the job is setup to allow that.
I have two processes. One is a producer that writes data to a FIFO file opened in O_RDWR mode. The other process is a consumer . It opens the FIFO in "read mode" using a file pointer.
When producer writes data to FIFO , consumer is reading the data from the FIFO using getline. When producer stops writing data , getline returns -1 with "ferror". After 2-3 hours with producer not writing any data to the FIFO , the getline call blocks the consumer process.
Can anyone explain why this is happening?
I'm using resque, with a queue processor which, as part of its execution, will start a shell process. Currently, I am using PTY.spawn() to invoke the shell command and handle its output.
I'd like to augment this code so that a quantity (N) can be given (the command executed onboards VMs, I want to be able to start a variable number with one call), and have the shell process be called N times in separate processes, without the Nth call having to wait for call N-1 to finish, and so on. I also want to capture all STDOUT from each invocation, so that I can do work on the output once the call is done.
I have looked at Kernel::fork but the scope of code inside a forked block is not the same as its parent (for pretty obvious reasons).
What tool(s) can I use so that each process can be spawned independently, their output can be captured, and I can still have the parent process wait for them all to finish before moving on?
Here:
stdouts=[]
numberOfProcesses.times do
stdouts<<PTY.spawn(command_line)[0..-1]
end
That's pretty basic if you just spawn them and get a bunch of STDOUT/STDIN pairs. If you want to be able to work on each process's output as soon as it is done, try this:
threads=[]
numberOfProcesses.times do
threads<<Thread.new(command_line) |cmd|
stdout, stdin, pid = PTY.spawn(cmd)
Process.waitpid(pid)
process_output(stdout.read)
end
end
threads.each {|t| t.join}
That spawns them in parallel, each thread waiting for when it's instance is done. When it's instance is done, it processes output and returns. The main thread sits waiting for all of the others to finish.
How can I handle CTRL+C in PHP on the command line? Pcntl_* functions do not work in Windows.
The following works on unix systems.
We can catch keys using stream_get_contents(), but it does not catch the CTRL key. Also filtering ^C does not works.
What we need to do is to catch the SIGINT posix signal.
To supress CTRL + c default behavior.
Program won't quit, you need then to implement another way of exiting!:
function shutdown(){};
pcntl_signal(SIGINT,"shutdown");
To handle CTRL + c, and run some code before exiting:
function shutdown(){
echo "\033c"; // Clear terminal
system("tput cnorm && tput cup 0 0 && stty echo"); // Restore cursor default
echo PHP_EOL; // New line
exit; // Clean quit
}
register_shutdown_function("shutdown"); // Handle END of script
declare(ticks = 1); // Allow posix signal handling
pcntl_signal(SIGINT,"shutdown"); // Catch SIGINT, run shutdown()
List of POSIX signals:
Php won't catch SIGKILL, can't be.
SIGABRT and SIGIOT
The SIGABRT and SIGIOT signal is sent to a process to tell it to abort, i.e. to terminate. The signal is usually initiated by the process itself when it calls abort() function of the C Standard Library, but it can be sent to the process from outside like any other signal.
SIGALRM, SIGVTALRM and SIGPROF
The SIGALRM, SIGVTALRM and SIGPROF signal is sent to a process when the time limit specified in a call to a preceding alarm setting function (such as setitimer) elapses. SIGALRM is sent when real or clock time elapses. SIGVTALRM is sent when CPU time used by the process elapses. SIGPROF is sent when CPU time used by the process and by the system on behalf of the process elapses.
SIGBUS
The SIGBUS signal is sent to a process when it causes a bus error. The conditions that lead to the signal being sent are, for example, incorrect memory access alignment or non-existent physical address.
SIGCHLD
The SIGCHLD signal is sent to a process when a child process terminates, is interrupted, or resumes after being interrupted. One common usage of the signal is to instruct the operating system to clean up the resources used by a child process after its termination without an explicit call to the wait system call.
SIGCONT
The SIGCONT signal instructs the operating system to continue (restart) a process previously paused by the SIGSTOP or SIGTSTP signal. One important use of this signal is in job control in the Unix shell.
SIGFPE
The SIGFPE signal is sent to a process when it executes an erroneous arithmetic operation, such as division by zero. This may include integer division by zero, and integer overflow in the result of a divide (only INT_MIN/-1, INT64_MIN/-1 and %-1 accessible from C).[2][3].
SIGHUP
The SIGHUP signal is sent to a process when its controlling terminal is closed. It was originally designed to notify the process of a serial line drop (a hangup). In modern systems, this signal usually means that the controlling pseudo or virtual terminal has been closed.[4] Many daemons will reload their configuration files and reopen their logfiles instead of exiting when receiving this signal.[5] nohup is a command to make a command ignore the signal.
SIGILL
The SIGILL signal is sent to a process when it attempts to execute an illegal, malformed, unknown, or privileged instruction.
SIGINT
The SIGINT signal is sent to a process by its controlling terminal when a user wishes to interrupt the process. This is typically initiated by pressing Ctrl+C, but on some systems, the "delete" character or "break" key can be used.[6]
SIGKILL
The SIGKILL signal is sent to a process to cause it to terminate immediately (kill). In contrast to SIGTERM and SIGINT, this signal cannot be caught or ignored, and the receiving process cannot perform any clean-up upon receiving this signal. The following exceptions apply:
Zombie processes cannot be killed since they are already dead and waiting for their parent processes to reap them.
Processes that are in the blocked state will not die until they wake up again.
The init process is special: It does not get signals that it does not want to handle, and thus it can ignore SIGKILL.[7] An exception from this exception is while init is ptraced on Linux.[8][9]
An uninterruptibly sleeping process may not terminate (and free its resources) even when sent SIGKILL. This is one of the few cases in which a UNIX system may have to be rebooted to solve a temporary software problem.
SIGKILL is used as a last resort when terminating processes in most system shutdown procedures if it does not voluntarily exit in response to SIGTERM. To speed the computer shutdown procedure, Mac OS X 10.6, aka Snow Leopard, will send SIGKILL to applications that have marked themselves "clean" resulting in faster shutdown times with, presumably, no ill effects.[10] The command killall -9 has a similar, while dangerous effect, when executed e.g. in Linux; it doesn't let programs save unsaved data. It has other options, and with none, uses the safer SIGTERM signal.
SIGPIPE
The SIGPIPE signal is sent to a process when it attempts to write to a pipe without a process connected to the other end.
SIGPOLL
The SIGPOLL signal is sent when an event occurred on an explicitly watched file descriptor.[11] Using it effectively leads to making asynchronous I/O requests since the kernel will poll the descriptor in place of the caller. It provides an alternative to active polling.
SIGRTMIN to SIGRTMAX
The SIGRTMIN to SIGRTMAX signals are intended to be used for user-defined purposes. They are real-time signals.
SIGQUIT
The SIGQUIT signal is sent to a process by its controlling terminal when the user requests that the process quit and perform a core dump.
SIGSEGV
The SIGSEGV signal is sent to a process when it makes an invalid virtual memory reference, or segmentation fault, i.e. when it performs a segmentation violation.[12]
SIGSTOP
The SIGSTOP signal instructs the operating system to stop a process for later resumption.
SIGSYS
The SIGSYS signal is sent to a process when it passes a bad argument to a system call. In practice, this kind of signal is rarely encountered since applications rely on libraries (e.g. libc) to make the call for them. SIGSYS can be received by applications violating the Linux Seccomp security rules configured to restrict them.
SIGTERM
The SIGTERM signal is sent to a process to request its termination. Unlike the SIGKILL signal, it can be caught and interpreted or ignored by the process. This allows the process to perform nice termination releasing resources and saving state if appropriate. SIGINT is nearly identical to SIGTERM.
SIGTSTP
The SIGTSTP signal is sent to a process by its controlling terminal to request it to stop (terminal stop). It is commonly initiated by the user pressing Ctrl+Z. Unlike SIGSTOP, the process can register a signal handler for, or ignore, the signal.
SIGTTIN and SIGTTOU
The SIGTTIN and SIGTTOU signals are sent to a process when it attempts to read in or write out respectively from the tty while in the background. Typically, these signals are received only by processes under job control; daemons do not have controlling terminals and, therefore, should never receive these signals.
SIGTRAP
The SIGTRAP signal is sent to a process when an exception (or trap) occurs: a condition that a debugger has requested to be informed of – for example, when a particular function is executed, or when a particular variable changes value.
SIGURG
The SIGURG signal is sent to a process when a socket has urgent or out-of-band data available to read.
SIGUSR1 and SIGUSR2
The SIGUSR1 and SIGUSR2 signals are sent to a process to indicate user-defined conditions.
SIGXCPU
The SIGXCPU signal is sent to a process when it has used up the CPU for a duration that exceeds a certain predetermined user-settable value.[13] The arrival of a SIGXCPU signal provides the receiving process a chance to quickly save any intermediate results and to exit gracefully, before it is terminated by the operating system using the SIGKILL signal.
SIGXFSZ
The SIGXFSZ signal is sent to a process when it grows a file that exceeds the maximum allowed size.
SIGWINCH
The SIGWINCH signal is sent to a process when its controlling terminal changes its size (a window change).[14]
As of PHP 7.4, this is now possible by registering a handler callback with the sapi_windows_set_ctrl_handler() function.
This is complemented by sapi_windows_generate_ctrl_event(), which can be used to dispatch signals to other processes attached to the same console as the caller.
Only the CTRL-C and CTRL-BREAK events can be handled in user space, the close/log-off/shutdown events cannot be implented safely as the operating system will likely be in an unpredictable state of partial shutdown by the time the handler function is invoked, so there is a risk that any code executed at this point will do more harm than good.
You can find more information about the underlying mechanism on MSDN:
SetConsoleCtrlHandler()
GenerateConsoleCtrlEvent()
The PHP API is almost identical to the underlying C API, the only notable difference being that PHP only permits a single callback to be registered, and consequently the handler does does not have a meaningful return value, the engine simply marks the events as handled. This is in order to keep the implementation simple, as a stack of functions can easily be implemented in userland, and likewise if you don't want to handle an event you can simply call exit.
If you want to run a task in PHP via command line that takes a very long time, I would try to organize it in badges and keep track of what is already done.
Now you can completely process each badge (ex: process and then store it in an xml file) and not only after the whole list is processed. So a crash/stop in between will only cancel one badge and not all of them.
If you store your current position after each badge somewhere, you can easily resume when your script crashes or is stopped.
Now if you check the OS process-list to see if your script is running, you can write a cron job that starts your script every X minutes if it had crashed and was not already running.
So, TL;DR
Process job in small badges
Store position of last successfully processed badge
Check for already running process at start
Continually start script until all are happy!
That aside, I like PHP for small command line jobs but if you have such a large task, something else might be better suited. Check for something that can run stable for a long time and has a means of showing it's progress. Maybe a small C# app with a minimalistic gui.
I'm having a deadlock on closing a pipe:
close(myPipeFD);
Another thread, the reading thread, is in a blocking read state from this exact same pipe:
ssize_t sizeRead = read(myPipeFD, buffer, bufferSize);
Could it be the cause of such deadlock? I thought that read would have immediately returned sizeRead == 0? Should I emit an interruption in this reading thread?
It is not safe to close a file descriptor when another thread may be using it, for several reasons.
As you've discovered, some system calls which can block waiting on the file descriptor may behave in unexpected ways if that file descriptor is closed.
But there are other problems. Let's suppose that the first thread closes a file descriptor just before a second thread enters a read() call on it. Let's also suppose that a third thread happens to be opening a file or a socket at the same time. The new file descriptor will get the same number as the one that was just closed. The second thread will read from the wrong file descriptor!
In general, you need to make sure that only one thread is operating on a file descriptor at a time. Threads should "own" file descriptors. You can pass ownership from one thread to another, but only one should own each at a time.
If you need to cancel operations, you need to use non-blocking I/O and things like select() for when you need to block waiting for data. Furthermore, you need to include a cross-thread communication channel (e.g. pipe) in the select() call which will be the mechanism by which one thread submits a request to the other to close one of its file descriptors.
You should also look into Dispatch I/O or asynchronous mechanisms like run-loop driven NSFileHandle.