Working With Unix Processes

Working With Unix Processes

Jesse Storimer

Language: English

Pages: 115


Format: PDF / Kindle (mobi) / ePub

A crash course in Unix programming for the uninitiated. Working With Unix Processes (WWUP for short) is a look at programming with the building blocks of a Unix system, something that's been done for decades. WWUP is the only book addressing Unix programming specifically for the modern web developer.

Learn the semantics of powerful concepts like forking, signals, file descriptors, daemon processes, and more.

With the included appendices you'll learn how popular Ruby projects are using these concepts to drive thousands of applications. These take the concepts presented and put them in a real-world context.

There are lots of great resources available on this topic for free on the web, so why does this book exist? This book is a short, to-the-point introduction written specifically for the modern web developer. All of the examples in the book are written in Ruby, no C programming required. Even though it's Ruby, anyone with experience in a high-level language should feel right at home.

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shipped | less In this case each command will get its own process group, since each may be creating child processes but none is a child process of another. Even though these commands are not part of the same process group one Ctrl-C will kill them all. These commands are part of the same session group. Each invocation from the shell gets its own session group. An invocation may be a single command or a string of commands joined by pipes. Like in the above example, a session group may be

controlling terminal and will run to its completion. Dir.chdir "/" This changes the current working directory to the root directory for the system. This isn't strictly necessary but it's an extra step to ensure that current working directory of the daemon doesn't disappear during it's execution. This avoids problems where the directory that the daemon was started from gets deleted or unmounted for any reason. STDIN.reopen "/dev/null" STDOUT.reopen "/dev/null", "a" STDERR.reopen "/dev/null",

#{}" Notice that both the if and else block make a call to procline. Even though these two lines are part of the same logical construct they are being executed in two different processes. Since the process name is process-specific these two calls will set the name for the parent and child process respectively. perform(job, &block) Here in the child process is where the job is actually 'performed' by Resque. exit! unless @cant_fork Then the child process exits. Why

[Spyglass::Worker] Received connection System Calls Ruby's maps to getpid(2). There is also a global variable that holds the value of the current pid. You can access it with $$. Ruby inherits this behaviour from other languages before it (both Perl and bash support $$), however I avoid it when possible. Typing out in full is much more expressive of your intent than the dollar-dollar variable, and less likely to confuse those who haven't seen the dollar-dollar

itself programmatically. Up until now we've talked about creating processes by launching them from the terminal. We've also mentioned low level operating system processes that create other processes: fork(2) is how they do it. When forking, the process that initiates the fork(2) is called the "parent", and the newly created process is called the "child". The child process inherits a copy of all of the memory in use by the parent process, as well as any open file descriptors belonging to the

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