更新简介说明

andrewbytecoder · andrewbytecoder · commit 422eec4f34f0 · 2023-11-14T18:55:54.000+08:00
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -34,7 +34,7 @@ else (WIN32)
     set(LEVELDB_PLATFORM_NAME LEVELDB_PLATFORM_POSIX)
 endif (WIN32)
 
-option(LEVELDB_BUILD_TESTS "Build LevelDB's unit tests" ON)
+option(LEVELDB_BUILD_TESTS "Build LevelDB's unit tests" OFF)
 option(LEVELDB_BUILD_BENCHMARKS "Build LevelDB's benchmarks" ON)
 option(LEVELDB_INSTALL "Install LevelDB's header and library" ON)
 
diff --git a/demo/CMakeLists.txt b/demo/CMakeLists.txt
@@ -13,4 +13,10 @@ target_include_directories(leveldb_exec
         PUBLIC ${PROJECT_SOURCE_DIR}/../include)
 
 
-add_executable(dataTest test.cpp)
+add_executable(test test.cpp)
+
+target_link_libraries(test
+        PUBLIC leveldb)
+
+target_include_directories(test
+        PUBLIC ${PROJECT_SOURCE_DIR}/../include)
diff --git a/demo/test.cpp b/demo/test.cpp
@@ -12,7 +12,10 @@
 #include <utility>
 #include <thread>
 #include <set>
-
+#include <iostream>
+#include <cassert>
+#include "leveldb/write_batch.h"
+#include "leveldb/db.h"
 
 using namespace std;
 
@@ -21,24 +24,8 @@ const uint64_t CREATE_SQL_STR_LEN = 1024 * 1024;
 
 int main(int argc, char *argv[]) {
 
-
-    std::set<std::string> newSet{};
-    newSet.insert("3");
-    newSet.insert("4");
-    newSet.insert("5");
-    newSet.insert("7");
-    newSet.insert("1");
-    newSet.insert("2");
-    newSet.insert("2");
-
-
-    for (auto& s : newSet) {
-        std::cout << s << std::endl;
-    }
-
-
-
-
+    int *lpData = nullptr;
+    std::cout << sizeof(*lpData) << std::endl;
 
 
     return 0;
diff --git a/doc/db/table_format.adoc b/doc/db/table_format.adoc
@@ -21,8 +21,7 @@ ifndef::rootpath[]
 endif::rootpath[]
 
 
-leveldb File format
-===================
+== leveldb File format
 
     <beginning_of_file>
     [data block 1]
@@ -37,7 +36,7 @@ leveldb File format
     [Footer]        (fixed size; starts at file_size - sizeof(Footer))
     <end_of_file>
 
-The file contains internal pointers.  Each such pointer is called
+The file contains internal pointers.Each such pointer is called
 a BlockHandle and contains the following information:
 
     offset:   varint64
diff --git a/doc/instruction/impl.adoc b/doc/instruction/impl.adoc
@@ -21,48 +21,8 @@ ifndef::rootpath[]
 endif::rootpath[]
 
 
-## Files
+== 基本概念
 
 
-### Log files
-
-
-
-## Sorted tables
-
-
-
-### Manifest
-
-
-### Current
-
-
-### Info logs
-
-
-### Others
-
-
-## Level 0
-
-
-
-## Compactions
-
-
-
-### Timing
-
-
-### Number of files
-
-
-## Recovery
-
-
-
-## Garbage collection of files
-
 
 
diff --git a/doc/instruction/readme.adoc b/doc/instruction/readme.adoc
@@ -148,7 +148,7 @@ options.error_if_exists = true;
 
 === 执行结果 Status
 
-在levelBD中你随处可见Status，该对象就是levelDB对返回值进行封装时候的结果，用来返回各种接口的执行情况
+在levelDB中你随处可见Status，该对象就是levelDB对返回值进行封装时候的结果，用来返回各种接口的执行情况
 
 [source, cpp]
 ----
@@ -157,35 +157,41 @@ if (!s.ok()) cerr << s.ToString() << endl;
 ----
 
 
-## Closing A Database
+== 如何关闭一个levelDB数据库
 
-When you are done with a database, just delete the database object. Example:
+当想关闭一个levelDB数据库时只需要调用delete将db删除即可。
 
-```c++
+[source,c++]
+----
 ... open the db as described above ...
 ... do something with db ...
 delete db;
-```
+----
 
-## Reads And Writes
+== 数据库的读写
 
-The database provides Put, Delete, and Get methods to modify/query the database.
-For example, the following code moves the value stored under key1 to key2.
+levelDB提供了Put/Delete/Get等接口来对数据库进行操作。
 
-```c++
+[source,c++]
+----
 std::string value;
+// 1. 去除key1的值
 leveldb::Status s = db->Get(leveldb::ReadOptions(), key1, &value);
+// 将key2的值设置为key1的值
 if (s.ok()) s = db->Put(leveldb::WriteOptions(), key2, value);
+// 删除key1
 if (s.ok()) s = db->Delete(leveldb::WriteOptions(), key1);
-```
+----
 
-## Atomic Updates
+== 原子操作(事务类型)
 
-Note that if the process dies after the Put of key2 but before the delete of
-key1, the same value may be left stored under multiple keys. Such problems can
-be avoided by using the `WriteBatch` class to atomically apply a set of updates:
+[listing]
+....
+上述将Key1的值设置给key2并删除Key1总共经过了三步，如果在删除key1之前数据库崩溃或被强制停掉了就会导致value存在key1和key2中。为了避免这种异常情况的出现，我们可以将上述三种情况作为一个原子操作。levelDB中可以通过WriteBatch来实现对多个步骤进行原子操作
+....
 
-```c++
+[source,c++]
+----
 #include "leveldb/write_batch.h"
 ...
 std::string value;
@@ -196,10 +202,10 @@ if (s.ok()) {
   batch.Put(key2, value);
   s = db->Write(leveldb::WriteOptions(), &batch);
 }
-```
+----
 
 The `WriteBatch` holds a sequence of edits to be made to the database, and these
-edits within the batch are applied in order. Note that we called Delete before
+edits within the batch are applied in order.Note that we called Delete before
 Put so that if key1 is identical to key2, we do not end up erroneously dropping
 the value entirely.
 
diff --git a/doc/utils/c++_common_knowledge.adoc b/doc/utils/c++_common_knowledge.adoc
@@ -107,6 +107,16 @@ class NoDestructor {
 
 ----
 
+
+=== sizeof
+
+需要注意的是，sizeof中* + 指针变量，并不是对指针变量的解引用，只是去除指针指向对象类型的意思，因此下面的代码并不会崩溃，而是给出指针指向对象的大小。
+[source, cpp]
+----
+int *lpData = nullptr;
+std::cout << sizeof(*lpData) << std::endl;
+----
+
 *总结*
 
 在整个levelDB中有很多地方都用了这个特性进行单例的创建，在这个实例的创建中使用了三个比较重要的C++知识点，alignof取结构体对齐长度，`new（placement new）` 来实现预分配内存的new，在结合 `aligned_storage` 来保证已有对象内存绝对大于等于需要申请对象的内存，然后经过饿汉式单例模式封装，经过以上几个步骤之后，一个能长久陪伴数据库句柄的对比工具便诞生了。
