From af671c44903b1fb7368976abace32823d982136c Mon Sep 17 00:00:00 2001
From: RexKnight <10152130255@stu.ecnu.edu.cn>
Date: Mon, 4 Dec 2017 21:44:08 +0800
Subject: [PATCH] Comments and clean

1. Add comments to almost all places (except futex, xchg and cmpxchg)
2. Delete all error checks for concurrent libraries. These libraries are mainly used to test performance of locks, implement error check will introduce irrelavent factors.
2. Clean unused codes and CLion files
3. Create Makefile (without -Wall and -Werror)
TODO: eliminate all warnings.
---
 .idea/OSLab-P4.iml                         |   2 -
 .idea/misc.xml                             |   4 -
 .idea/modules.xml                          |   8 -
 .idea/vcs.xml                              |   6 -
 .idea/workspace.xml                        | 507 ---------------------
 cmake-build-debug/CMakeFiles/clion-log.txt |   1 -
 error.h                                    |  13 -
 src/CMakeLists.txt                         |   9 +
 src/Makefile                               |  14 +
 src/counter.c                              |  40 +-
 src/counter.h                              |   4 +-
 src/hash.c                                 |  56 +--
 src/hash.h                                 |  14 +-
 src/list.c                                 |  60 +--
 src/list.h                                 |  19 +-
 src/lock.c                                 | 271 ++++++-----
 src/lock.h                                 |  82 ++--
 src/main.c                                 |  11 +-
 18 files changed, 290 insertions(+), 831 deletions(-)
 delete mode 100644 .idea/OSLab-P4.iml
 delete mode 100644 .idea/misc.xml
 delete mode 100644 .idea/modules.xml
 delete mode 100644 .idea/vcs.xml
 delete mode 100644 .idea/workspace.xml
 delete mode 100644 cmake-build-debug/CMakeFiles/clion-log.txt
 delete mode 100644 error.h
 create mode 100644 src/CMakeLists.txt
 create mode 100644 src/Makefile

diff --git a/.idea/OSLab-P4.iml b/.idea/OSLab-P4.iml
deleted file mode 100644
index f08604b..0000000
--- a/.idea/OSLab-P4.iml
+++ /dev/null
@@ -1,2 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module classpath="CMake" type="CPP_MODULE" version="4" />
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
deleted file mode 100644
index 79b3c94..0000000
--- a/.idea/misc.xml
+++ /dev/null
@@ -1,4 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="CMakeWorkspace" PROJECT_DIR="$PROJECT_DIR$" />
-</project>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
deleted file mode 100644
index 9f3dfc8..0000000
--- a/.idea/modules.xml
+++ /dev/null
@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="ProjectModuleManager">
-    <modules>
-      <module fileurl="file://$PROJECT_DIR$/.idea/OSLab-P4.iml" filepath="$PROJECT_DIR$/.idea/OSLab-P4.iml" />
-    </modules>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
deleted file mode 100644
index 94a25f7..0000000
--- a/.idea/vcs.xml
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="VcsDirectoryMappings">
-    <mapping directory="$PROJECT_DIR$" vcs="Git" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
deleted file mode 100644
index 54d0539..0000000
--- a/.idea/workspace.xml
+++ /dev/null
@@ -1,507 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="CMakeRunConfigurationManager" shouldGenerate="true" shouldDeleteObsolete="true" buildAllGenerated="false">
-    <generated />
-  </component>
-  <component name="CMakeSettings">
-    <configurations>
-      <configuration CONFIG_NAME="Debug" />
-    </configurations>
-  </component>
-  <component name="ChangeListManager">
-    <list default="true" id="70d5bd6c-68bf-4c4e-9294-a6609c3caa38" name="Default" comment="" />
-    <ignored path="$PROJECT_DIR$/cmake-build-debug/" />
-    <option name="EXCLUDED_CONVERTED_TO_IGNORED" value="true" />
-    <option name="TRACKING_ENABLED" value="true" />
-    <option name="SHOW_DIALOG" value="false" />
-    <option name="HIGHLIGHT_CONFLICTS" value="true" />
-    <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
-    <option name="LAST_RESOLUTION" value="IGNORE" />
-  </component>
-  <component name="FileEditorManager">
-    <leaf SIDE_TABS_SIZE_LIMIT_KEY="300">
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-  <component name="JsBuildToolPackageJson" detection-done="true" sorting="DEFINITION_ORDER" />
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-    <option name="width" value="1400" />
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diff --git a/cmake-build-debug/CMakeFiles/clion-log.txt b/cmake-build-debug/CMakeFiles/clion-log.txt
deleted file mode 100644
index 48f35e9..0000000
--- a/cmake-build-debug/CMakeFiles/clion-log.txt
+++ /dev/null
@@ -1 +0,0 @@
-CMakeLists.txt not found in E:\Github\OSLab\OSLab-P4
diff --git a/error.h b/error.h
deleted file mode 100644
index 15547cd..0000000
--- a/error.h
+++ /dev/null
@@ -1,13 +0,0 @@
-//
-// Created by Sean on 2017/12/2.
-//
-
-#ifndef OSLAB_P4_ERROR_H
-#define OSLAB_P4_ERROR_H
-
-#define E_NO_CORRESPONDING_VALUE 1551
-#define E_DATA_OVERFLOW 1919
-
-int user_error;
-
-#endif //OSLAB_P4_ERROR_H
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..2aa3450
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,9 @@
+cmake_minimum_required(VERSION 3.8)
+project(P4)
+
+set(CMAKE_CXX_STANDARD 11)
+
+find_package (Threads)
+set(SOURCE_FILES main.c lock.h counter.h list.h hash.h lock.c counter.c list.c hash.c)
+add_executable(P4 ${SOURCE_FILES})
+target_link_libraries (P4 ${CMAKE_THREAD_LIBS_INIT})
\ No newline at end of file
diff --git a/src/Makefile b/src/Makefile
new file mode 100644
index 0000000..037fcf4
--- /dev/null
+++ b/src/Makefile
@@ -0,0 +1,14 @@
+make: libcounter.so liblist.so libhash.so
+
+P4:
+	export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
+	cc -lcounter -llist -lhash -L. -o P4 main.c libcounter.so liblist.so libhash.so -lpthread
+
+libcounter.so:
+	cc -shared -fPIC counter.c lock.h lock.c -o libcounter.so
+
+liblist.so:
+	cc -shared -fPIC list.c lock.h lock.c -o liblist.so
+
+libhash.so:
+	cc -shared -fPIC hash.c list.h list.c lock.h lock.c -o libhash.so
diff --git a/src/counter.c b/src/counter.c
index 2c4e792..9068819 100644
--- a/src/counter.c
+++ b/src/counter.c
@@ -1,23 +1,21 @@
 #include "counter.h"
 
-extern int user_error;
-
 /**
- *  Initialization part of counter
- * @param c a pointer to a counter
+ * Initialization part of counter
+ * @param c pointer to a counter
  * @param value Initial value of the counter
  */
-void counter_init(counter_t* c, int value) {
+void counter_init(counter_t *c, int value) {
     c->value = value;
     lock_init(&c->lock);
 }
 
 /**
- *  Get the value of the counter
- * @param c a pointer to a counter
- * @return the value of the counter
+ * Get the value of the counter
+ * @param c pointer to a counter
+ * @return the current value of the counter
  */
-int counter_get_value(counter_t* c) {
+int counter_get_value(counter_t *c) {
 #if defined(LOCK_RWLOCK)
     rwlock_rdlock(&c->lock);
 #else
@@ -29,37 +27,29 @@ int counter_get_value(counter_t* c) {
 }
 
 /**
- *  Make the counter's value increase by 1
- * @param c a pointer to a counter
+ * Increase the counter by 1
+ * @param c pointer to a counter
  */
-void counter_increment(counter_t* c) {
+void counter_increment(counter_t *c) {
 #if defined(LOCK_RWLOCK)
     rwlock_wrlock(&c->lock);
 #else
     lock_acquire(&c->lock);
 #endif
-    if (c->value == INT_MAX) {
-        user_error = E_DATA_OVERFLOW;
-    }else {
-        c->value++;
-    }
+    c->value++;
     lock_release(&c->lock);
 }
 
 /**
- *  Make the counter's value increase by 1
- * @param c a pointer to a counter
+ * Decrease the counter by 1
+ * @param c pointer to a counter
  */
-void counter_decrement(counter_t* c) {
+void counter_decrement(counter_t *c) {
 #if defined(LOCK_RWLOCK)
     rwlock_wrlock(&c->lock);
 #else
     lock_acquire(&c->lock);
 #endif
-    if (c->value == INT_MIN) {
-        user_error = E_DATA_OVERFLOW;
-    }else {
-        c->value--;
-    }
+    c->value--;
     lock_release(&c->lock);
 }
diff --git a/src/counter.h b/src/counter.h
index b4643fd..d61fb4d 100644
--- a/src/counter.h
+++ b/src/counter.h
@@ -2,10 +2,10 @@
 #define P4_COUNTER_H
 
 #include "lock.h"
-#define INT_MAX 2147483647
-#define INT_MIN (-INT_MAX - 1)
+
 /**
  * A concurrent counter type
+ * All operations except initialization are thread-safe
  */
 typedef struct {
     int value;    /**< internal counter variable */
diff --git a/src/hash.c b/src/hash.c
index 39e2ce2..420adbe 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -1,26 +1,11 @@
 #include "hash.h"
 
 /**
- * Initialize hash table with given bucket size
- * will call perror to print error message once malloc fail
+ * Initialize the hash table with given bucket size
  * @param hash A pointer to hash table
  * @param size designated bucket size
- *//*
-void hash_init(hash_t *hash, int size, unsigned int threshold) {    // hash_init with threshold
-    hash->lists = malloc(sizeof(list_t)*size);
-    if (hash->lists == NULL) {
-        perror("malloc");
-        return;
-    }
-    int i;
-    hash->bucket_size = size;
-    hash->threshold = threshold;
-    for (i = 0; i < size; i++) {
-        list_init(&hash->lists[i]);
-    }
-    //lock_init(&hash->lock);
-}*/
-void hash_init(hash_t *hash, int size) {    // hash_init without threshold
+ */
+void hash_init(hash_t *hash, int size) {
     int i;
     hash->bucket_size = size;
     hash->lists = malloc(sizeof(list_t)*size);
@@ -42,7 +27,7 @@ void hash_insert(hash_t *hash, unsigned int key) {
 
 /**
  * Delete a key into hash table
- * if multiple keys detected in hash table, only delete one of them
+ * If multiple keys detected in hash table, only delete one of them
  * @param hash The pointer to hash table
  * @param key The key to be deleted
  */
@@ -55,7 +40,7 @@ void hash_delete(hash_t *hash, unsigned int key) {
  * Find a given key in hash table
  * @param hash The pointer to hash table
  * @param key The key to find
- * @return A pointer to node contains given key, should a into node_t before use.
+ * @return A pointer to the node with given key, should cast to node_t type before use.
  */
 void* hash_lookup(hash_t *hash, unsigned int key) {
     int bucket = key % hash->bucket_size;
@@ -63,7 +48,7 @@ void* hash_lookup(hash_t *hash, unsigned int key) {
 }
 
 /**
- * remove an given hash table and free the pointer of it
+ * Remove an given hash table and free the pointer of it
  * @param hash The pointer to hash table
  */
 void* hash_destroy(hash_t *hash) {
@@ -73,32 +58,3 @@ void* hash_destroy(hash_t *hash) {
     }
     free(hash->lists);
 }
-
-/**
- * Check whether the total length of the hash table has exceeded the threshold
- * if so resize the hash table and destory the previous one
- * @param hash The pointer to a hash table
- */
-void hash_resize(hash_t *hash) {
-    unsigned int i, tmp_key, length = 0;
-    for (i = 0; i < hash->bucket_size; ++i) {
-        length += list_count(&hash->lists[i]);
-    }
-    if (length < hash->threshold) {
-        return;
-    }
-    hash_t new_hash;
-    hash_init(&new_hash, length*2, 2*hash->threshold);
-    for (i = 0; i < hash->bucket_size; ++i) {
-        list_t tmp_list = hash->lists[i];
-        node_t *cur = tmp_list.head;
-        while (cur != NULL) {
-            tmp_key = cur->key;
-            hash_insert(&new_hash, tmp_key);
-            cur = cur->next;
-        }
-    }
-    hash_t* hash_old = hash;
-    hash = &new_hash;
-    hash_destroy(hash_old);
-}
\ No newline at end of file
diff --git a/src/hash.h b/src/hash.h
index aaa4c9a..04681e9 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -3,19 +3,21 @@
 
 #include "list.h"
 
+/**
+ * The concurrent hash definition
+ * The hash function is simply module bucket size (but effective)
+ * This implementation need no more parallel protection since list is already thread-safe
+ * All operations except initialize and destroy are thread-safe
+ */
 typedef struct {
-    list_t *lists;
-    int bucket_size;
-    //lock_t lock;
-    //unsigned int threshold;
+    list_t *lists;   /**< lists for hash buckets */
+    int bucket_size; /**< the bucket size designated when initialized, can't be changed during use */
 } hash_t;
 
-//void hash_init(hash_t *hash, int size, unsigned int threshold);
 void hash_init(hash_t *hash, int size);
 void hash_insert(hash_t *hash, unsigned int key);
 void hash_delete(hash_t *hash, unsigned int key);
 void *hash_lookup(hash_t *hash, unsigned int key);
 void* hash_destroy(hash_t *hash);
-//void hash_resize(hash_t *hash);
 
 #endif //P4_HASH_H
diff --git a/src/list.c b/src/list.c
index 5e3642a..7325b3f 100644
--- a/src/list.c
+++ b/src/list.c
@@ -1,7 +1,4 @@
 #include "list.h"
-#include <stdio.h>
-
-extern int user_error;
 
 /**
  * Initialize the given list
@@ -19,38 +16,29 @@ void list_init(list_t *list) {
  */
 void list_insert(list_t *list, unsigned int key) {
     node_t *new_node = malloc(sizeof(node_t));
-    if (newNode == NULL) {
-        perror("malloc");
-        return;
-    }
     new_node->key = key;
-    //printf("%ld In insert1\n", pthread_self()%10000);
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_wrlock(&list->lock);
 #else
     lock_acquire(&list->lock);
 #endif
-    //printf("%ld In insert2\n", pthread_self()%10000);
     new_node->next = list->head;
     list->head = new_node;
-    //printf("%ld Out insert1\n", pthread_self()%10000);
     lock_release(&list->lock);
-    //printf("%ld Out insert2\n", pthread_self()%10000);
 }
 
 /**
- * Delete the node with value key
+ * Delete one node with the given value
+ * If multiple targets are found, only delete one of them
  * @param list A pointer to a list
  * @param key The key value of the node to be deleted
  */
 void list_delete(list_t* list, unsigned int key) {
-    //printf("%ld In delete1\n", pthread_self()%10000);
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_wrlock(&list->lock);
 #else
     lock_acquire(&list->lock);
 #endif
-    //printf("%ld In delete2\n", pthread_self()%10000);
     node_t* cur = list->head;
     node_t* pre = NULL;
     while (cur != NULL) {
@@ -67,30 +55,25 @@ void list_delete(list_t* list, unsigned int key) {
             list->head = cur->next;
         }
         free(cur);
-    }else {
-        user_error = E_NO_CORRESPONDING_VALUE;
     }
-    //printf("%ld out delete1\n", pthread_self()%10000);
     lock_release(&list->lock);
-    //printf("%ld out delete2\n", pthread_self()%10000);
 }
 
 /**
- *  Find out whether there is a node with a value of key.
- *  If there is, return the pointer to the node with value key,
- *  return NULL otherwise
+ * Find out whether there exists a node with the given key.
+ * If found, return a pointer to the target node.
+ * Otherwise, return NULL instead.
+ *
  * @param list A pointer to a list
  * @param key The key value of the node to be lookup
- * @return A pointer to the node with value key
+ * @return A pointer to the node with given key, should cast to node_t type before use.
  */
 void* list_lookup(list_t* list, unsigned int key) {
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_rdlock(&list->lock);
 #else
     lock_acquire(&list->lock);
 #endif
-    //printf("%ld In lookup1\n", pthread_self()%10000);
-    //printf("%ld In lookup2\n", pthread_self()%10000);
     node_t* cur = list->head;
     while (cur != NULL) {
         if (cur->key == key) {
@@ -98,19 +81,17 @@ void* list_lookup(list_t* list, unsigned int key) {
         }
         cur = cur->next;
     }
-    //printf("%ld Out lookup1\n", pthread_self()%10000);
     lock_release(&list->lock);
-    //printf("%ld Out lookup2\n", pthread_self()%10000);
     return cur;
 }
 
 /**
- *  Calculate the total number of nodes in list
+ * Calculate the total number of nodes in this list
  * @param list A pointer to a list
- * @return the total number of nodes in list
+ * @return The total number of nodes in the list
  */
 int list_count(list_t* list) {
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_rdlock(&list->lock);
 #else
     lock_acquire(&list->lock);
@@ -118,9 +99,6 @@ int list_count(list_t* list) {
     int cnt = 0;
     node_t *cur = list->head;
     while (cur != NULL) {
-        if (cnt == INT_MIN) {
-            user_error = E_DATA_OVERFLOW;
-        }
         cnt++;
         cur = cur->next;
     }
@@ -129,12 +107,12 @@ int list_count(list_t* list) {
 }
 
 /**
- *  Calculate the sum of all nodes' value
+ * Calculate the sum of all nodes' key field
  * @param list A pointer to a list
- * @return the sum of all nodes' value
+ * @return The sum of all nodes' value
  */
 long long list_sum(list_t* list) {
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_rdlock(&list->lock);
 #else
     lock_acquire(&list->lock);
@@ -150,11 +128,11 @@ long long list_sum(list_t* list) {
 }
 
 /**
- *  Destroy the given list
- * @param list A pointer to a list
+ * Destroy the given list
+ * @param list The list to be deleted
  */
 void list_destroy(list_t* list) {
-#if defined(LOCK_RWLOCK)
+#if defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_wrlock(&list->lock);
 #else
     lock_acquire(&list->lock);
diff --git a/src/list.h b/src/list.h
index 0648e73..8f8b19f 100644
--- a/src/list.h
+++ b/src/list.h
@@ -4,16 +4,25 @@
 #include "lock.h"
 #include <stdio.h>
 #include <stdlib.h>
-#define INT_MAX 2147483647
 
+/**
+ * Node type in the list
+ *
+ */
 typedef struct _node_t {
-    unsigned int key;
-    struct _node_t *next;
+    unsigned int key;     /**< the key field of this node */
+    struct _node_t *next; /**< pointer to the next node in the list */
 } node_t;
 
+
+/**
+ * A concurrent list definition
+ * All operations except initialization and destroy are thread-safe
+ * Maintain a head-insert linked-list
+ */
 typedef struct {
-    node_t *head;
-    lock_t lock;
+    node_t *head; /**< a pointer to the head node */
+    lock_t lock;  /**< guarantee sequential execution in list functions */
 } list_t;
 
 void list_init(list_t *list);
diff --git a/src/lock.c b/src/lock.c
index 81e4ab2..2f0a232 100644
--- a/src/lock.c
+++ b/src/lock.c
@@ -8,25 +8,27 @@
 
 // struct timespec wait_time = { 1, 0 };
 
+#define atomic_add(P, V) __sync_add_and_fetch((P), (V))
+
+
 static long sys_futex(void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3) {
     return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
 }
 
+/**
+ * Pause the cpu core using assembly code to avoid bad performance on some machine
+ */
 static inline void cpu_pause(void) {
-    asm volatile("rep; nop" : : : "memory");
-    //asm volatile("pause\n": : :"memory");
+    //asm volatile("rep; nop" : : : "memory");
+    asm volatile("pause\n": : :"memory");
 }
 
-/*
-static inline uint xchg(volatile unsigned int *addr, unsigned int newval) {
-    uint result;
-    asm volatile("lock; xchgl %0, %1"
-    : "+m" (*addr), "=a" (result)
-    : "1" (newval)
-    : "cc");
-    return result;
-}*/
-
+/**
+ * Exchange value in addr and newval atomically
+ * @param addr   The
+ * @param newval
+ * @return
+ */
 static inline unsigned xchg(void *addr, unsigned newval) {
     asm volatile("xchgl %0, %1"
     : "=r" (newval)
@@ -44,45 +46,80 @@ static inline uint cmpxchg(volatile unsigned int *addr, unsigned int oldval, uns
     return ret;
 }
 
+/**
+ * Initialize a spin-lock, should be called before use
+ * @param lock Pointer to the spin-lock need to be initialized
+ */
 void spinlock_init(spinlock_t* lock) {
-    lock->flag = 0;
+    *lock = 0;
 }
 
+/**
+ * Try to acquire the given spin-lock
+ * If the lock currently not available, this function will keep trying until somebody release the lock
+ * @param lock Pointer to the spin-lock want to obtain
+ */
 void spinlock_acquire(spinlock_t *lock) {
-    while (xchg(&lock->flag, 1) == 1) {
+    while (xchg(lock, 1) == 1) {
         cpu_pause(); // spin-wait
     }
 }
 
+/**
+ * Release the given spin-lock
+ * Notice that release a lock not hold by itself will cause unpredictable result
+ * @param lock Pointer to the spin-lock want to release
+ */
 void spinlock_release(spinlock_t *lock) {
-    lock->flag = 0;
+    *lock = 0;
 }
 
+/**
+ * Initialize a mutex, should be called before use
+ * @param lock Pointer to the mutex need to be initialized
+ */
 void mutex_init(mutex_t *lock) {
     *lock = 0;
 }
 
+/**
+ * Try to acquire the given mutex
+ * A failed try will cause the thread sleep until another thread wake it by releasing this mutex
+ * @param lock Pointer to the mutex want to obtain
+ */
 void mutex_acquire(mutex_t *lock) {
     int value = xchg(lock, 1);
     while (value) {
-        //printf("%d lock rd: %d\n", pthread_self()%10000, value);
         sys_futex(lock, FUTEX_WAIT_PRIVATE, 1, NULL, NULL, 0);
         value = xchg(lock, 1);
     }
-    //printf("%d locked\n", pthread_self()%10000);
 }
 
+/**
+ * Release the given mutex
+ * Notice that release a lock not hold by itself will cause unpredictable result
+ * @param lock Pointer to the spin-lock want to release
+ */
 void mutex_release(mutex_t *lock) {
-    while (xchg(lock, 0)) ;
-    //printf("%d unlock : %d\n", pthread_self()%10000, *lock);
+    xchg(lock, 0);
     sys_futex(lock, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
 }
 
+/**
+ * Initialize a two-phase lock, should be called before use
+ * @param lock Pointer to the lock need to be initialized
+ */
 void twophase_init(twophase_t *lock) {
     *lock = 0;
 }
 
-#define LOOP_MAX 1000
+/**
+ * Try to acquire the given two-phase lock
+ * Wait for some one to release first, the wait time is designated by the LOOP_MAX macro (defined below)
+ * If the lock still acquired by someone else after wait phase, it will sleep until someone release the lock
+ * @param lock Pointer to the two-phase lock want to obtain
+ */
+#define LOOP_MAX 100
 void twophase_acquire(twophase_t *lock) {
     int i, value = 1;
     for (i = 0; i < LOOP_MAX; i++) {
@@ -92,16 +129,22 @@ void twophase_acquire(twophase_t *lock) {
         }
         cpu_pause();
     }
+
     if (value == 1) {
         value = xchg(lock, 2);
     }
-
     while (value) {
         sys_futex(lock, FUTEX_WAIT_PRIVATE, 2, NULL, NULL, 0);
         value = xchg(lock, 2);
     }
 }
 
+/**
+ * Release the given two-phase lock
+ * In the first phase it will try to give the lock to someone awake
+ * If failed, it will wake up a sleeping thread on this lock
+ * @param lock Pointer to the two-phase lock want to release
+ */
 void twophase_release(twophase_t *lock) {
     int i;
 
@@ -112,56 +155,83 @@ void twophase_release(twophase_t *lock) {
     }
 
     for (i = 0; i < LOOP_MAX; i++) {
-        if (*lock && cmpxchg(lock, 1, 2)) {
-            return;
+        if (*lock) {
+            if (cmpxchg(lock, 1, 2)) {
+                return;
+            }
         }
+        cpu_pause();
     }
 
     sys_futex(lock, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
 }
 
-
-void cond_init(cond_t* lock) {
-    lock->seq = 0;
-    lock->mutex = NULL;
+/**
+ * Initialize a condition variable, should be called before use
+ * @param cv Pointer to the condition variable need to be initialized
+ */
+void cond_init(cond_t* cv) {
+    cv->seq = 0;
+    cv->mutex = NULL;
 }
 
-void cond_wait(cond_t* lock, mutex_t* mutex) {
-    int old_seq = lock->seq;
-
-    if (lock->mutex != mutex) {
-        if (lock->mutex != NULL) { // TODO: ERROR
+/**
+ * Wait a thread on the given condition variable
+ * The caller will sleep on the given cv, its mutex will be released
+ * Note that the mutex should be two-phase type since cv need extra information in mutex
+ * @param cv    Pointer the the condition variable to wait on
+ * @param mutex The mutex owned by caller, will be released
+ */
+void cond_wait(cond_t* cv, twophase_t* mutex) {
+    int old_seq = cv->seq;
+
+    if (cv->mutex != mutex) {
+        if (cv->mutex != NULL) { // TODO: ERROR
             return;
         }
-        cmpxchg(&lock->mutex, NULL, mutex);
-        if (lock->mutex != mutex) { // TODO: ERROR
+        cmpxchg(&cv->mutex, NULL, mutex);
+        if (cv->mutex != mutex) { // TODO: ERROR
             return;
         }
     }
 
-    mutex_release(mutex);
+    twophase_release(mutex);
 
-    sys_futex(&lock->seq, FUTEX_WAIT, old_seq, NULL, NULL, 0);
+    sys_futex(&cv->seq, FUTEX_WAIT_PRIVATE, old_seq, NULL, NULL, 0);
 
     while (xchg(mutex, 2)) {
-        sys_futex(mutex, FUTEX_WAIT, 2, NULL, NULL, 0);
+        sys_futex(mutex, FUTEX_WAIT_PRIVATE, 2, NULL, NULL, 0);
     }
 }
 
-void cond_signal(cond_t* lock) {
-    lock->seq++;
-    sys_futex(&lock->seq, FUTEX_WAKE, 1, NULL, NULL, 0);
+/**
+ * Wake up a thread waiting on the given condition variable
+ * @param cv The condition variable to receive a signal
+ */
+void cond_signal(cond_t* cv) {
+    atomic_add(&cv->seq, 1);
+    sys_futex(&cv->seq, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
 }
 
-void cond_broadcast(cond_t* lock) {
-    mutex_t* old_mutex = lock->mutex;
+/**
+ * Wake up ALL threads waiting on the given condition variable
+ * @param cv The condition variable to receive a broadcast
+ */
+void cond_broadcast(cond_t* cv) {
+    mutex_t* old_mutex = cv->mutex;
     if (old_mutex == NULL) {
         return;
     }
-    lock->seq++;
-    sys_futex(&lock->seq, FUTEX_REQUEUE, 1, (void*)2147483647, old_mutex, 0);
+    atomic_add(&cv->seq, 1);
+
+    // wake up 1 waiting thread, requeue other threads on mutex to avoid context switch
+    sys_futex(&cv->seq, FUTEX_REQUEUE_PRIVATE, 1, (void*) 0x0FFFFFFF, old_mutex, 0);
 }
 
+/**
+ * Initialize a read-write lock, should be called before use
+ * @param lock Pointer to the read-write lock need to be initialized
+ */
 void rwlock_init(rwlock_t* lock) {
 #if defined(LOCK_PRWLOCK)
     pthread_rwlock_init(lock, NULL);
@@ -170,116 +240,82 @@ void rwlock_init(rwlock_t* lock) {
     lock->writers = 0;
     lock->read_waiters = 0;
     lock->write_waiters = 0;
-    mutex_init(&lock->mutex);
-
-    lock->writer_preferred = 1; // enable this to prefer writer
-#elif defined(LOCK_RWLOCK2)
-    lock->readers = 0;
-    lock->writers = 0;
-    lock->read_waiters = 0;
-    lock->write_waiters = 0;
-    mutex_init(&lock->mutex);
+    twophase_init(&lock->mutex);
     cond_init(&lock->reader_lock);
     cond_init(&lock->writer_lock);
 #endif
 }
 
+/**
+ * Acquire the read-end of the given read-write lock
+ * @param lock Pointer to the read-write lock to be acquired
+ */
 void rwlock_rdlock(rwlock_t *lock) {
 #if defined(LOCK_PRWLOCK)
     pthread_rwlock_rdlock(lock);
 #elif defined(LOCK_RWLOCK)
-    mutex_acquire(&lock->mutex);
-    while (lock->writers || (lock->write_waiters && lock->writer_preferred)) {
-        lock->read_waiters++;
-        mutex_release(&lock->mutex);
-        sys_futex(&lock->read_waiters, FUTEX_WAIT_PRIVATE, 1, NULL, NULL, 0);
-        mutex_acquire(&lock->mutex);
-        lock->read_waiters--;
-    }
-    lock->readers++;
-    mutex_release(&lock->mutex);
-#elif defined(LOCK_RWLOCK2)
-    mutex_acquire(&lock->mutex);
+    twophase_acquire(&lock->mutex);
     while (lock->writers || lock->write_waiters) {
         lock->read_waiters++;
         cond_wait(&lock->reader_lock, &lock->mutex);
         lock->read_waiters--;
     }
     lock->readers++;
-    mutex_release(&lock->mutex);
+    twophase_release(&lock->mutex);
 #endif
 }
 
+/**
+ * Acquire the write-end of the given read-write lock
+ * @param lock Pointer to the read-write lock to be acquired
+ */
 void rwlock_wrlock(rwlock_t *lock) {
 #if defined(LOCK_PRWLOCK)
     pthread_rwlock_wrlock(lock);
 #elif defined(LOCK_RWLOCK)
-    mutex_acquire(&lock->mutex);
-    while (lock->readers || lock->writers) {
-        lock->write_waiters++;
-        mutex_release(&lock->mutex);
-        sys_futex(&lock->write_waiters, FUTEX_WAIT_PRIVATE, 1, NULL, NULL, 0);
-        mutex_acquire(&lock->mutex);
-        lock->write_waiters--;
-    }
-    lock->writers = 1;
-    mutex_release(&lock->mutex);
-#elif defined(LOCK_RWLOCK2)
-    mutex_acquire(&lock->mutex);
+    twophase_acquire(&lock->mutex);
     while (lock->readers || lock->writers) {
         lock->write_waiters++;
         cond_wait(&lock->writer_lock, &lock->mutex);
         lock->write_waiters--;
     }
     lock->writers = 1;
-    mutex_release(&lock->mutex);
+    twophase_release(&lock->mutex);
 #endif
 }
 
+/**
+ * Release the read-write lock, for both read and write end according to POSIX standard
+ * Note this implement slightly favour the writers
+ * @param lock Pointer to the read-write to be released
+ */
 void rwlock_unlock(rwlock_t* lock) {
 #if defined(LOCK_PRWLOCK)
     pthread_rwlock_unlock(lock);
 #elif defined(LOCK_RWLOCK)
-    mutex_acquire(&lock->mutex);
-    if (lock->readers) { // if there're readers
+    twophase_acquire(&lock->mutex);
+    if (lock->readers) {
         lock->readers--;
-        if (lock->readers) { // if still have other readers
-            mutex_release(&lock->readers);
-            return;
+        if (lock->write_waiters) {
+            cond_signal(&lock->writer_lock);
         }
-    } else {
+    } else if (lock->writers) {
         lock->writers = 0;
-    }
-    mutex_release(&lock->mutex);
-
-    if (lock->write_waiters) { // wake a writer first
-        sys_futex(&lock->write_waiters, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
-    } else if (lock->read_waiters) { // wake all readers
-        sys_futex(&lock->read_waiters, FUTEX_WAKE_PRIVATE, 2147483647, NULL, NULL, 0);
-    }
-
-#elif defined(LOCK_RWLOCK2)
-    mutex_acquire(&lock->mutex);
-    if (lock->readers) { // if there're readers
-        lock->readers--;
-        if (lock->readers) { // if still have other readers
-            mutex_release(&lock->readers);
-            return;
+        if (lock->write_waiters) {
+            cond_signal(&lock->writer_lock);
+        } else if (lock->read_waiters) {
+            cond_broadcast(&lock->reader_lock);
         }
-    } else {
-        lock->writers = 0;
-    }
-    mutex_release(&lock->mutex);
-
-    if (lock->write_waiters) { // wake a writer first
-        cond_signal(&lock->writer_lock);
-    } else if (lock->read_waiters) { // wake all readers
-        cond_broadcast(&lock->reader_lock);
     }
+    twophase_release(&lock->mutex);
 #endif
 }
 
-
+/**
+ * The generic lock initialization method, not use macro for the debug consideration
+ * The lock type is designated by the macros defined in header file
+ * @param lock A pointer to the lock to be initialized
+ */
 void lock_init(lock_t* lock) {
 #if defined(LOCK_MUTEX)
     mutex_init(lock);
@@ -289,11 +325,16 @@ void lock_init(lock_t* lock) {
     twophase_init(lock);
 #elif defined(LOCK_PTHREAD)
     pthread_mutex_init(lock, NULL);
-#elif defined(LOCK_RWLOCK)
+#elif defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_init(lock);
 #endif
 }
 
+/**
+ * The generic lock acquire method
+ * Note that read-write locks DO NOT call this function
+ * @param lock A pointer to the lock to be acquired
+ */
 void lock_acquire(lock_t* lock) {
 #if defined(LOCK_MUTEX)
     mutex_acquire(lock);
@@ -306,6 +347,10 @@ void lock_acquire(lock_t* lock) {
 #endif
 }
 
+/**
+ * The generic lock release method
+ * @param lock A pointer to the lock to be released
+ */
 void lock_release(lock_t* lock) {
 #if defined(LOCK_MUTEX)
     mutex_release(lock);
@@ -315,7 +360,7 @@ void lock_release(lock_t* lock) {
     twophase_release(lock);
 #elif defined(LOCK_PTHREAD)
     pthread_mutex_unlock(lock);
-#elif defined(LOCK_RWLOCK)
+#elif defined(LOCK_RWLOCK) || defined(LOCK_PRWLOCK)
     rwlock_unlock(lock);
 #endif
 }
diff --git a/src/lock.h b/src/lock.h
index f3df0c6..2b58609 100644
--- a/src/lock.h
+++ b/src/lock.h
@@ -3,67 +3,63 @@
 
 #include <pthread.h>
 
-/* The following 4 lock types are exclusive
- * select one of them and comment others to enable specific lock implement
- * note that rwlock will not implement lock_acquire and lock_release
- * rwlock also rewrite implements of counter and list
+/**
+ * The following 6 lock types are exclusive
+ * Select one of them and comment others to enable specific implementation for generic lock
+ * Note that rwlock will not implement lock_acquire, but rewrite implements of counter and list instead
+ * Also note that pthread rwlock rewrite rwlock implement
  */
-//#define LOCK_MUTEX
 //#define LOCK_SPIN
+//#define LOCK_MUTEX
 //#define LOCK_TWOPHASE
-//#define LOCK_RWLOCK
-#define LOCK_RWLOCK2
+#define LOCK_RWLOCK
 //#define LOCK_PTHREAD
 //#define LOCK_PRWLOCK
 
-typedef struct {
-    unsigned int flag;
-} spinlock_t;
+/**
+ * The following 3 lock type definitions are trivial, just literal meaning
+ */
+typedef unsigned int spinlock_t;
 
 typedef unsigned int mutex_t;
 
 typedef unsigned int twophase_t;
 
-/*
-typedef union {
-    unsigned int value;
-    struct {
-        unsigned char locked;
-        unsigned char contended;
-    } bit_set;
-} twophase_t;
-*/
-
+/**
+ * Condition variable is a kind of synchronization means
+ * Can cause threads wait on a specific condition
+ * Also can wake one or all waiting thread(s) easily
+ */
 typedef struct {
-    unsigned seq;
-    mutex_t *mutex;
+    unsigned seq;      /**< sequence number used to judge cv status */
+    twophase_t *mutex; /**< serialize operations on cv */
 } cond_t;
 
+/**
+ * Read-write lock is designed to parallel read threads instead of sequential execution
+ * This implement use condition variable to wait/wake and requeue sleeping threads
+ */
 #if defined(LOCK_PRWLOCK)
 typedef pthread_rwlock_t rwlock_t;
 #elif defined(LOCK_RWLOCK)
 typedef struct {
-    mutex_t mutex;
-    char writer_preferred;
-    unsigned readers;
-    unsigned writers;
-    unsigned read_waiters;
-    unsigned write_waiters;
-} rwlock_t;
-#elif defined(LOCK_RWLOCK2)
-typedef struct {
-    mutex_t mutex;
-    cond_t reader_lock;
-    cond_t writer_lock;
-    unsigned readers;
-    unsigned writers;
-    unsigned read_waiters;
-    unsigned write_waiters;
+    twophase_t mutex;       /**< serialize operations on rwlock */
+    cond_t reader_lock;     /**< the cv for readers */
+    cond_t writer_lock;     /**< the cv for writers */
+    unsigned readers;       /**< reader counter */
+    unsigned writers;       /**< writer counter, should only be 0 or 1 */
+    unsigned read_waiters;  /**< counter for waiters on the read end */
+    unsigned write_waiters; /**< counter for waiters on the write end */
 } rwlock_t;
 #else
 typedef int rwlock_t;
 #endif
 
+
+/**
+ * The generic lock type definition
+ * Directly use existing lock types
+ */
 #if defined(LOCK_MUTEX)
 typedef mutex_t lock_t;
 #elif defined(LOCK_SPIN)
@@ -72,8 +68,6 @@ typedef spinlock_t lock_t;
 typedef twophase_t lock_t;
 #elif defined(LOCK_RWLOCK)
 typedef rwlock_t lock_t;
-#elif defined(LOCK_RWLOCK2)
-typedef rwlock_t lock_t;
 #elif defined(LOCK_PTHREAD)
 typedef pthread_mutex_t lock_t;
 #elif defined(LOCK_PRWLOCK)
@@ -94,10 +88,10 @@ void twophase_init(twophase_t *lock);
 void twophase_acquire(twophase_t *lock);
 void twophase_release(twophase_t *lock);
 
-void cond_init(cond_t* lock);
-void cond_wait(cond_t* lock, mutex_t* mutex);
-void cond_signal(cond_t* lock);
-void cond_broadcast(cond_t* lock);
+void cond_init(cond_t* cv);
+void cond_wait(cond_t* cv, twophase_t* mutex);
+void cond_signal(cond_t* cv);
+void cond_broadcast(cond_t* cv);
 
 void rwlock_init(rwlock_t* self);
 void rwlock_rdlock(rwlock_t *lock);
diff --git a/src/main.c b/src/main.c
index fd99a64..85763d6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -19,8 +19,8 @@ double endTimer() {
     return (tve.tv_sec - tvb.tv_sec) * 1000 + (tve.tv_usec - tvb.tv_usec) / 1000.0;
 }
 
-#define THREAD_COUNT 8
-#define MAX_N 10000
+#define THREAD_COUNT 4
+#define MAX_N 100000
 #define SEED 1234
 
 counter_t counter;
@@ -41,9 +41,9 @@ void* test(void* args) {
 
 void* test2(void* args) {
     printf("thread %d to sleep.\n", (int)args);
-    mutex_acquire(&mutex);
+    twophase_acquire(&mutex);
     cond_wait(&cond, &mutex);
-    mutex_release(&mutex);
+    twophase_release(&mutex);
     test_var = test_var + 1;
     printf("thread %d waked.\n", (int)args);
     return NULL;
@@ -69,6 +69,7 @@ void* test4(void* args) {
     srand(SEED);
     for (i = 0; i < MAX_N; i++) {
         int rd = rand() % 100;
+        //pthread_mutex_lock(&p_mutex);
         if (rd < READ_RATE) {
             list_lookup(&list, rand() % RANGE);
         } else if (rd < READ_RATE + INSERT_RATE) {
@@ -88,6 +89,7 @@ void* test4(void* args) {
                 pthread_mutex_unlock(&p_mutex);
             }
         }
+        //pthread_mutex_unlock(&p_mutex);
     }
     return NULL;
 }
@@ -126,6 +128,7 @@ void main1() {
 void main2() {
     int i;
     test_var = 0;
+    mutex_init(&mutex);
     cond_init(&cond);
     pthread_t* threads = malloc(sizeof(pthread_t)*THREAD_COUNT);
     startTimer();