From 6923dc7fbaddf392375973fd5d7327ae1e83bedc Mon Sep 17 00:00:00 2001
From: Weicheng <weicheng.pei@icloud.com>
Date: Sat, 31 Aug 2024 18:47:02 +0800
Subject: [PATCH] Implement a pool using `pthread_mutex_t`.

---
 programming/csapp/labs/proxy/pool.c | 60 +++++++++++++++++++++++++++++
 programming/csapp/labs/proxy/pool.h | 18 +++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 programming/csapp/labs/proxy/pool.c
 create mode 100644 programming/csapp/labs/proxy/pool.h

diff --git a/programming/csapp/labs/proxy/pool.c b/programming/csapp/labs/proxy/pool.c
new file mode 100644
index 0000000..a1f6c0d
--- /dev/null
+++ b/programming/csapp/labs/proxy/pool.c
@@ -0,0 +1,60 @@
+#include "csapp.h"
+#include "pool.h"
+
+#include <pthread.h>
+
+// For non-static initialization.
+static pthread_once_t once = PTHREAD_ONCE_INIT;
+static pthread_mutex_t *_mutex;  // should be guarded by a mutex, too
+void mutex_init() {
+    pthread_mutex_init(_mutex, NULL);
+}
+
+struct _pool {
+    /* a FIFO queue */
+    int *buf;          /* Buffer array */
+    int n;             /* Maximum number of slots */
+    int front;         /* buf[(front+1)%n] is first item */
+    int rear;          /* buf[rear%n] is last item */
+    /* queue and counting semaphores */
+    pthread_mutex_t queue;  /* Protects accesses to the queue. */
+    sem_t slots;  /* Counts available slots. */
+    sem_t items;  /* Counts available items. */
+};
+
+/* Create an empty, bounded, shared FIFO buffer with n slots */
+void pool_init(pool_t *p, int n) {
+    p->buf = Calloc(n, sizeof(int));
+    p->n = n;                   /* Buffer holds max of n items */
+    p->front = p->rear = 0;     /* Empty buffer iff front == rear */
+    _mutex = &p->queue;
+    pthread_once(&once, mutex_init);
+    Sem_init(&p->slots, 0, n);  /* Initially, buf has n empty slots */
+    Sem_init(&p->items, 0, 0);  /* Initially, buf has zero data items */
+}
+
+/* Clean up buffer p */
+void pool_deinit(pool_t *p) {
+    Free(p->buf);
+    pthread_mutex_destroy(&p->queue);
+}
+
+/* Insert item onto the rear of shared buffer p */
+void pool_insert(pool_t *p, int item) {
+    P(&p->slots);                       /* Wait for available slot */
+    pthread_mutex_lock(&p->queue);      /* Lock the buffer */
+    p->buf[(++p->rear)%(p->n)] = item;  /* Insert the item */
+    pthread_mutex_unlock(&p->queue);    /* Unlock the buffer */
+    V(&p->items);                       /* Announce available item */
+}
+
+/* Remove and return the first item from buffer p */
+int pool_remove(pool_t *p) {
+    int item;
+    P(&p->items);                        /* Wait for available item */
+    pthread_mutex_lock(&p->queue);       /* Lock the buffer */
+    item = p->buf[(++p->front)%(p->n)];  /* Remove the item */
+    pthread_mutex_unlock(&p->queue);     /* Unlock the buffer */
+    V(&p->slots);                        /* Announce available slot */
+    return item;
+}
diff --git a/programming/csapp/labs/proxy/pool.h b/programming/csapp/labs/proxy/pool.h
new file mode 100644
index 0000000..326bbf9
--- /dev/null
+++ b/programming/csapp/labs/proxy/pool.h
@@ -0,0 +1,18 @@
+/**
+ * @file pool.h
+ * @brief Mimic `pool.h` but using `pthread_mutex_t`.
+ * 
+ */
+
+#ifndef __POOL__
+#define __POOL__
+
+struct _pool;
+typedef struct _pool pool_t;
+
+void pool_init(pool_t *p, int n);
+void pool_deinit(pool_t *p);
+void pool_insert(pool_t *p, int item);
+int pool_remove(pool_t *p);
+
+#endif /* __POOL__ */