Definition
type Builder struct {
// contains filtered or unexported fields
}
A Builder is used to efficiently build a string using Write methods. It minimizes memory copying. The zero value is ready to use. Do not copy a non-zero Builder.
...【Golang】使用 - Concatenate String
Clean and simple string building
For simple cases where performance is a non-issue, fmt.Sprintf is your friend. It’s clean, simple and fairly efficient.
s := fmt.Sprintf("Size: %d MB.", 85) // s == "Size: 85 MB."
【Operating System】进程 - 进程间通讯 - Memory Barrier/Fence
Memory Barrier/Fence
A memory barrier, also known as a membar, memory fence or fence instruction, is a type of barrier instruction that causes a central processing unit (CPU) or compiler to enforce an ordering constraint on memory operations issued before and after the barrier instruction. This typically means that operations issued prior to the barrier are guaranteed to be performed before operations issued after the barrier.
Memory barriers are necessary because most modern CPUs employ performance optimizations that can result in out-of-order execution. This reordering of memory operations (loads and stores) normally goes unnoticed within a single thread of execution, but can cause unpredictable behaviour in concurrent programs and device drivers unless carefully controlled. The exact nature of an ordering constraint is hardware dependent and defined by the architecture’s memory ordering model. Some architectures provide multiple barriers for enforcing different ordering constraints.
- Java Memory Model: https://swsmile.info/post/java-memory-model/
- Golang Memory Model: https://swsmile.info/post/golang-memory-model/
【Operating System】进程 - 上下文切换
Switching cases
There are three potential triggers for a context switch:
Multitasking
Most commonly, within some scheduling scheme, one process must be switched out of the CPU so another process can run. This context switch can be triggered by the process making itself unrunnable, such as by waiting for an I/O or synchronization operation to complete.
On a pre-emptive multitasking system, the scheduler may also switch out processes that are still runnable. To prevent other processes from being starved of CPU time, pre-emptive schedulers often configure a timer interrupt to fire when a process exceeds its time slice. This interrupt ensures that the scheduler will gain control to perform a context switch.
...【Lock】自旋锁（Spinlock）
背景
在介绍自旋锁前，我们需要介绍一些前提知识来帮助大家明白自旋锁的概念。
阻塞或唤醒一个Java线程需要操作系统进行 context swtich（e.g., kernel space <-> user space, interrupt handling due to I/O or waiting for synchrnization operation to complete）来完成，
Refer to https://swsmile.info/post/os-context-swtich/ in details.
这种 context 转换需要耗费处理器时间。如果同步代码块中的内容过于简单，context 转换消耗的时间有可能比用户代码执行的时间还要长。
在许多场景中，同步资源的锁定时间很短，为了这一小段时间去切换线程，线程挂起和恢复现场的花费可能会让系统得不偿失。如果物理机器有多个处理器，能够让两个或以上的线程同时并行执行，我们就可以让后面那个请求锁的线程不放弃CPU的执行时间，看看持有锁的线程是否很快就会释放锁。
而为了让当前线程“稍等一下”，我们需让当前线程进行自旋，如果在自旋完成后前面锁定同步资源的线程已经释放了锁，那么当前线程就可以不必阻塞而是直接获取同步资源，从而避免切换线程的开销。这就是自旋锁。
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