读源码的实用技巧

1. 查看Java native方法源码

Java底层的native方法可以在OpenJDK中通过类名_方法名（方法名首字母要大写）的形式找到该方法对应的源码实现

eg：分配直接内存的方法ByteBuffer.allocateDirect(1024)源码跟下去会发现核心代码实现是Unsafe.class中的如下方法：

1	private native long allocateMemory0(long var1);

想要查看 Unsafe::allocateMemory0(long var1)的源码，可以在OpenJDK中搜索Unsafe_AllocateMemory0，如下：

UNSAFE_ENTRY(jlong, Unsafe_AllocateMemory0(JNIEnv *env, jobject unsafe, jlong size)) {
  size_t sz = (size_t)size;

  assert(is_aligned(sz, HeapWordSize), "sz not aligned");

  void* x = os::malloc(sz, mtOther);

  return addr_to_java(x);
} UNSAFE_END

2. 查看操作系统方法介绍

上述Unsafe_AllocateMemory0方法中核心实现方法为os::malloc(sz, mtOther)，malloc是操作系统的原生方法，此类方法可以借助Linux系统命令man $方法名来查看方法对应的手册条目介绍，如下（不同操作系统可能有略微差别）：

1	☁ ~ man malloc

MALLOC(3)                BSD Library Functions Manual                MALLOC(3)

NAME
     calloc, free, malloc, realloc, reallocf, valloc, aligned_alloc -- memory allocation

SYNOPSIS
     #include <stdlib.h>

     void *
     calloc(size_t count, size_t size);

     void
     free(void *ptr);

     void *
     malloc(size_t size);
        
        ...

DESCRIPTION
     The malloc(), calloc(), valloc(), realloc(), and reallocf() functions
     allocate memory.  The allocated memory is aligned such that it can be
     used for any data type, including AltiVec- and SSE-related types.  The
     aligned_alloc() function allocates memory with the requested alignment.
     The free() function frees allocations that were created via the preceding
     allocation functions.

     The malloc() function allocates size bytes of memory and returns a
     pointer to the allocated memory.
     ......

3. TODO 持续更新

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读源码的实用技巧

读源码的实用技巧

1. 查看Java native方法源码

2. 查看操作系统方法介绍

3. TODO 持续更新

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