From 7ea7075614f7ec2b6e0bc79dc9bfb13c42758e01 Mon Sep 17 00:00:00 2001
From: Jet Hughes <jethughes0@gmail.com>
Date: Thu, 29 Sep 2022 09:51:54 +1300
Subject: [PATCH] vault backup: 2022-09-29 09:51:54

---
 content/notes/17-processes-communication.md | 29 ++++++++++++++++++++-
 content/notes/cosc-204.md                   |  2 ++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/content/notes/17-processes-communication.md b/content/notes/17-processes-communication.md
index 27d04847a..c5638e4ee 100644
--- a/content/notes/17-processes-communication.md
+++ b/content/notes/17-processes-communication.md
@@ -4,6 +4,9 @@ aliases:
 tags: 
 - cosc204
 - lecture
+sr-due: 2022-10-02
+sr-interval: 3
+sr-ease: 250
 ---
 
 ![process tree example](https://i.imgur.com/4ysHisl.png)
@@ -41,6 +44,30 @@ automatically executes exit after the last statement.
 - all rsouces are dallocated by the OS
 
  they can also die more violently
- 
+ - `kill` command
+ - you can only processes you 'own'
+ - Orphan process: a process whose parent terminated (inherited by init)
+ - Zombie process: one which terminated, but its live parent process is not WAITING for it. Since no process is receiving its exit status, it stays in the process table
 
 # signal and pipe for inter process communication
+## signal
+communication between OS kernel and processes and between processes
+
+- process can install a handler (function) for a signal using the system call signaction() except for SIGKILL
+- The default action for a signal is usually to kill/terminate the process if a handler is not installed.
+- Other actions are ignore, core (dump a large file for debugging), stop(stop the process), and continue. The last two actions are used by debuggers like gdb to debug a program.
+
+![partial list of signals](https://i.imgur.com/MMCEPqW.png)
+
+
+## pipe
+connect process output and another process input. 
+
+uni-directional channel
+
+file descriptors
+- 0 - stdin
+- 1 - stdout
+- 2 - sterr
+
+you can make file descriptors point to the same file using dup/dup2/dup3
\ No newline at end of file
diff --git a/content/notes/cosc-204.md b/content/notes/cosc-204.md
index 342bd7a06..299898098 100644
--- a/content/notes/cosc-204.md
+++ b/content/notes/cosc-204.md
@@ -45,6 +45,8 @@ tags:
 - [14-processes-and-system-calls](notes/14-processes-and-system-calls.md)
 - [15-file-systems](notes/15-file-systems.md)
 - [16-device-drivers](notes/16-device-drivers.md)
+- [17-processes-communication](notes/17-processes-communication.md)
+- 
 
 # Archive