Dark Horse Programmer--Multi-line Cheng (i.)

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The relationship between multi-threading and CPU and memory

From Baidu know.

This answer I think is a good metaphor.

CPU is not at the same time in the process operation, we know that there are many processes in the Windows operating system, and the CPU is a one to operate these processes, of course, the multi-core CPU can be implemented at the same time to operate these processes, so why the more CPU cores the faster the computer is like this, But memory is a bottleneck and cannot exceed this amount of memory.

According to the above mentioned CPU is a one to control the process (high-speed switching), then there will be a problem, if we start multiple threads control the data inside a process, because the CPU is one of the processing, and the thread can be implemented concurrently, In case the CPU is just processing here and jumping to the other process, the thread that is starting is processing the data of the process, then there is a security risk, such as:

2 Threads control data for a process

One thread 1 executes the data of this process when the CPU is just switching, and thread 1 is suspended.

At this point, if thread 2 gets CPU execution, thread 2 executes the process data, and thread 1 is activated to execute the data.

int x = 1;

String name;

int money;

void Run ()

{

if (x > 0)//thread 1 is judged to be suspended, thread 2 entered to determine that the condition was met

{

x = x-1;

Name = "Kvieta, mind";

Money + = 1000;

Core code of the bank

......

}

}

According to the above code combined with the text description, then my account does not have 2000 dollars!

Workaround: Java provides a keyword synchronized, which includes two usages: Synchronized method and synchronized block

Refer to the API for details.

The synchronization function controls the entry and exit of the thread with this, and the synchronous static function controls the access of the thread to the byte-code file corresponding to the class to which the function belongs.

Dark Horse Programmer--Multi-line Cheng (i.)