vault backup: 2022-09-21 14:09:30

content/notes/14-processes-and-system-calls.md

@@ -41,7 +41,7 @@ system program types include.,
 
 also runs in user space
 
-## system calls
+# system calls
 processes issue requests to the kernel by making system calls
 
 ![system call diagram|300](https://i.imgur.com/GAktF7t.png)
@@ -105,6 +105,51 @@ generated by:
 
 a system call generates an interrupt and the OS transfers control to a system call handler
 
-### data structure of kernel process
+# Processes
+a process is dynamic
 
+a given program can be executing many times of a given machines: each instance is a separate process
 
+process components
+- text section/code section: the program code itself 
+- data section: any global variables used by the program 
+- process stack: any local variables currently being used 
+- program counter: a pointer to some place in the program code 
+- contents of CPU registers 
+- memory management information 
+- device/file allocation information 
+- accounting information
+
+## process control blocks
+the OS keeps a record of each process in the system, with a data structure called *process control block* (PCB)
+
+![example block|400](https://i.imgur.com/UTDFjse.png)
+
+![example linux processes|400](https://i.imgur.com/ar19swB.png)
+
+## scheduling processes
+processes take turns to run on the CPU. processes wait to run in one of two queues:
+- ready queue: process ready to execute
+- device queue: processes waiting to use a particular device. (one queue per device)
+
+generally represented as linked lists
+
+## flow of processes
+![process flow diagram|400](https://i.imgur.com/ib1t78H.png)
+
+Rounded rectangles are events. 
+Rectangles are queues where processes wait. 
+Circles are processing resources that serve the events/queues.
+
+## process creation
+created by another process: parent process creates a child process
+- process can copy itself using fork
+- child process can then call exec() to load a new program
+	- a child process can run concurrently with parent
+	- child process can share the resources of its parent if not restricted
+
+system start with one process called *init*
+
+## procees heirarchy
+processes for a tree
+![process tree diagram|400](https://i.imgur.com/SNTlCNZ.png)

content/notes/cosc-204.md

@@ -42,6 +42,7 @@ tags:
 - [11-struct-and-union](notes/11-struct-and-union.md)
 - [12-pointers-to-routines](notes/12-pointers-to-routines.md)
 - [13-OS-intro](notes/13-OS-intro.md)
+- [14-processes-and-system-calls](notes/14-processes-and-system-calls.md)
 
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