vault backup: 2022-10-12 09:59:42

content/notes/18-processes-sharing-and-threads.md

@@ -27,7 +27,7 @@ ptr = mmap(NULL, 10240, PROT_READ|PROT_WRITE,
 	MAP_SHARED | MAP_FILE, random_fd, 0);
 ```
 
-private mapping is often ysed to set up new memory sections.
+private mapping is often used to set up new memory sections.
 ``` c
 fd = open("mmap_test_file", O_RDWR); p
 tr = mmap(NULL, 10240, PROT_READ|PROT_WRITE, 
@@ -35,5 +35,59 @@ tr = mmap(NULL, 10240, PROT_READ|PROT_WRITE,
 ```
 
 
+
 # Threads
+
+## product consumer problem
+- a producer process writes data to a buffer of fied size
+- a consumer reads data from the buffer
+these two processes are being scheduled independently by the CPU
+
+producer must wait if buffer is full
+consumer must wait if buffer is empty
+
+## threads
+- allows more convenient data sharing
+- threads within a single process share everything except they have their own program counter, registers and stack space
+
+![diagram](https://i.imgur.com/XcLsWyd.png)
+
+## why
+- responsiveness - parrallelism - dont have to wait
+- resource sharing - automaticall share everything in same process
+- economy - lightweight, creating and switching between threads is faster than creating heavyweight processes
+- scalability - each to work on multiprocessor architectures
+
+## pthread
+- pthread_create(): create a thread 
+- pthread_exit(): terminate a thread 
+- pthread_join(): wait for a thread to terminate 
+- pthread_detach(): detach a thread so that it won’t be waited 
+- pthread_self(): get the thread id of the current thread 
+- pthread_equal(): compare if two threads are the same 
+- pthread_cancel(): send a cancellation request to a thread
+
+``` c
+void *myThreadFun(void *vargp) { 
+	sleep(1)
+	printf("Hello from Thread \n")
+	return NULL
+} 
+	
+int main() { 
+	pthread_t thread_id
+	printf("Before Thread\n")
+	pthread_create(&thread_id, NULL, myThreadFun, NULL)
+	pthread_join(thread_id, NULL)
+	printf("After Thread\n");
+	exit(0);
+}
+```
+
+## web server thread
+- a web server is a process that provides data over the web to requesting clients
+- a thread is created for each request
+
+
+
 Lightweight process - shares everything except the stack