Multi process programming in C Post: 302894454

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Top Forums Programming Multi process programming in C Post 302894454 by alister on Tuesday 25th of March 2014 02:08:48 PM

03-25-2014

Registered User

As before, I did not compile or test the code. There may be other issues.

content is allocated and freed but never used.

fd will never contain an error code; it's always a pointer value. When that pointer is NULL, it indicates an error and the error code is in errno. That's what you should be inspecting during error handling. To convert the integer errno into a useful message, something like strerror() will help.

As you discovered, inserting arbitrary text into a script can present serious issues. The simplest solution is to write the reminder's text to a separate file.

strcpy of optarg to text is unsafe and can overflow. You can use strncpy, but then must be careful to ensure that the string is always null-terminated. strlcpy is a simpler alternative, if available. However, the simplest alternative in this case is to not copy at all.

Not only do you not need to copy, you don't need to allocate either. The reminder's text has already been allocated storage during startup. It's in argv. The only thing you need to do is pass around the pointer. The default value has also been stored away in the executable's image and it's location can also be passed around.

You implied that you are no longer waiting in the parent, but since the code is still there, a couple of notes about it.

You should always check WIFEXITED before using WEXITSTATUS (as you did with WIFSIGNALED before using WTERMSIG). An implementation is not forbidden from overloading bits for signal and status information (though I don't know if any implementation actually does so).

For portability and readability (especially for readability), it's a far better choice to use the macros in signal.h. Instead of 6, use SIGABRT. As far as I know, even though the kill(1) utility is required to recognize -6 as SIGABRT, nothing requires the kill(2) system call implementation to equate 6 with SIGABRT (although it almost certainly does).

Regarding your interprocess communication question, your pid file idea seems perfectly reasonable.

Regards,
Alister

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rhino

RHINO(1)						      General Commands Manual							  RHINO(1)

NAME

       rhino - invokes the JavaScript shell for running scripts in batch mode or interactive

SYNOPSIS

       rhino [options] script_filename_or_url [script_arguments]

DESCRIPTION

       This  manual  page documents briefly the rhino command.	This manual page was written for the Debian distribution because the original pro-
       gram does not have a manual page. It is written according to the html documentation.

       rhino is a start script for the rhino JavaScript shell which provides a simple way to run scripts in batch mode or an interactive  environ-
       ment for exploratory programming.

OPTIONS

       -e script_source
	      Executes script_source as a JavaScript script.

       -f script_filename_or_url
	      Reads script_filename_or_url content and execute it as a JavaScript script.

       -opt, -O optLevel
	      Optimizes  at level optLevel, which must be an integer between -1 and 9. -1 means Interpretive mode is always used. 0 means no opti-
	      mizations whereas 9 means all optimizations are performed.

       -version versionNumber
	      Specifies the language version to compile with. The string versionNumber must be one of 100, 110, 120, 130, or 140.  See	JavaScript
	      Language Versions for more information on language versions.

       -strict
	      Enable strict mode.

PREDEFINED PROPERTIES

       Scripts executing in the shell have access to some additional properties of the top-level object.

       arguments
	      The arguments object is an array containing the strings of all the arguments given at the command line when the shell was invoked.

       help() Executing the help function will print usage and help messages.

       defineClass(className)
	      Define an extension using the Java class named with the string argument className. Uses ScriptableObject.defineClass() to define the
	      extension.

       deserialize(filename)
	      Restore from the specified file an object previously written by a call to serialize.

       load([filename,...])
	      Load JavaScript source files named by string arguments. If multiple arguments are given, each file is read in and executed in turn.

       loadClass(className)
	      Load and execute the class named by the string argument className. The class must be a class that implements the	Script	interface,
	      as will any script compiled by jsc.

       print([expr...])
	      Evaluate and print expressions. Evaluates each expression, converts the result to a string, and prints it.

       readFile(path[,characterCoding])
	      Read  given file and convert its bytes to a string using the specified character coding or default character coding if explicit cod-
	      ing argument is not given.

       readUrl(url[,characterCoding])
	      Open an input connection to the given string url, read all its bytes and convert them to a string using the specified character cod-
	      ing or default character coding if explicit coding argument is not given.

       runCommand(commandName,[arg,...][options])
	      Execute  the  specified command with the given argument and options as a separate process and return the exit status of the process.
	      For details, see JavaDoc for org.mozilla.javascript.tools.shell.Global#runCommand.

       serialize(object,filename)
	      Serialize the given object to the specified file.

       spawn(functionOrScript)
	      Run the given function or script in a different thread.

       sync(function)
	      creates a synchronized function (in the sense of a Java synchronized method) from an existing function. The  new	function  synchro-
	      nizes on the this object of its invocation.

       quit() Quit shell. The shell will also quit in interactive mode if an end-of-file character is typed at the prompt.

       version([number])
	      Get  or  set  JavaScript	version number. If no argument is supplied, the current version number is returned. If an argument is sup-
	      plied, it is expected to be one of 100, 110, 120, 130, or 140 to indicate JavaScript version 1.0, 1.1,  1.2,  1.3,  or  1.4  respec-
	      tively.

SEE ALSO

       The online documentation under http://www.mozilla.org/rhino/shell.html

AUTHOR

       This manual page was written by Wolfgang Baer <WBaer@gmx.de>, for the Debian project (but may be used by others).

								February  12, 2005							  RHINO(1)