汉森实现管程的实例
一、管程來解決生產(chǎn)者/消費者問題
1)
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Struct Monitor
{
condition NF,NE;
int Buffer[n];
int k = 0,t = 0,count = 0;
define Add(int),Remove(int);
use wait(),signal(),check(),release();
void init() //初始化局部變量和條件變量
{
count = 0;k = 0;t = 0;NF = 0;NE = 0;
}
vodi Add(int i)
{
check();
if(count ==n) wait(NF);
Buffer[k] = i;
k = (k+1)%n;
count++;
signal(NE);
release();
}
void Remove(int &i)
{
check();
if(count == 0)wait(NE);
i = Buffer[t];
t = (t+1)%n;
count–;
signal(NF);
release();
}
}
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process producteri()//i = 1,2…,m
{
int x;
x = 生產(chǎn)一個產(chǎn)品(整數(shù))
Add(x);
}
process consumerj()//j = 1,2,…,r
{
int x;
Remove(x);
消費該產(chǎn)品(整數(shù));
}
二、用管程來解決優(yōu)先寫著的讀者/寫著問題
優(yōu)先寫者的讀者/寫著問題要求是:
①讀者共享;
②寫著互斥;
③有讀者在讀,寫著不可寫;
④寫著在寫,讀者不可讀;
⑤當讀者在讀時,寫著提出寫的要求,后面的讀者就不允許進入讀文件;
⑥當里面的讀者讀完時,由寫著進入寫;
⑦當寫著寫完后,優(yōu)先喚醒等待的寫著,如果沒有寫著等待,才喚醒等待的讀者進行讀;
1)
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struct Monitor
{
condition RR,WW;
int ReaderCnt,WriterCnt;
define StartRead,EndRead,StartWrite,EndWrite;
use wait,signal,check,release;
void StartRead()
{
check();
if(WriterCnt>0)wait(RR);
ReaderCnt++;
signal(RR);
release();
}
void EndRead()
{
check();
ReaderCnt–;
if(ReaderCnt == 0)signal(WW);
release();
}
void StartWrite()
{
check();
WriterCnt++;
if(ReadCnt>0 || WriterCnt>1)wait(WW);
release();
}
void EndWrite()
{
check();
WriterCnt–;
if(WriterCnt>0)signal(WW);
else
signal(RR);
release();
}
void init()
{
ReaderCnt=0;WriterCnt=0;RR=0;WW=0;
}
}
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process reader()
{
ReadWriter.StartRead();
讀文件;
ReadWriter.EndRead();
}
process writer()
{
ReadWriter.StartWrite();
寫文件;
ReadWriter.EndWrite();
}
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