跪求大神解答

always_waiting

我目前在學(xué)習(xí)一個Perl模塊，叫threads::shared

在這個模塊里我對于cond_broadcast這個函數(shù)不是很理解。其實(shí)說實(shí)話，我對于多線程就不是很理解。
比如lock函數(shù)的作用是什么，為什么要有l(wèi)ock函數(shù)
同樣的cond_wait函數(shù)又有什么作用？
cond_signal和cond_broadcast函數(shù)呢？

我看了perl的幫助文檔，對于這些函數(shù)有一些理解，但是還是需要大神給予確定才行。

---

首先是lock函數(shù)
比如有如下代碼:
```
sub fun1{
    lock $public_var;
    ....
}
```
這樣一來，在多線程運(yùn)行時，當(dāng)運(yùn)行到lock這里時，其他函數(shù)不能對$public_var進(jìn)行修改，直到fun1函數(shù)運(yùn)行完成。

---

其次是cond_wait函數(shù)
比如有如下代碼：
```
sub fun2{
   cond_wait $public_var;
   ....
}
```
這樣一來，如果同一時間運(yùn)行fun1和fun2兩個函數(shù)，那么首先會在fun1中可以修改$public_var，運(yùn)行完fun1后，在fun2中可以修改$public_var。

是這樣嗎？我對這個函數(shù)理解不清晰......

---

最后是cond_signal和cond_broadcast
這兩個函數(shù)就完全沒有理解了.......

---

所以跪求大神給予指導(dǎo){:3_200:}

always_waiting

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always_waiting

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yeahnoob

LZ一開始關(guān)于lock和cond_wait 的內(nèi)容應(yīng)該是不正確的。
lock只是一個聲明性質(zhì)的函數(shù)，聲明出一個阻塞式變量，單獨(dú)不會直接影響sub的執(zhí)行。
cond_wait的實(shí)際用途，恰好是LZ一開始對lock函數(shù)理解的用途。

1. perldoc threads::shared

復(fù)制代碼

另外兩個cond_signal和cond_broadcast在perldoc里面我覺得說的是很清楚，

1. 
   
2.        cond_signal VARIABLE
   
3.            The "cond_signal" function takes a locked variable as a parameter and unblocks one thread that's "cond_wait"ing on that variable. If
   
4.            more than one thread is blocked in a "cond_wait" on that variable, only one (and which one is indeterminate) will be unblocked.
   
5. 
   
6.            If there are no threads blocked in a "cond_wait" on the variable, the signal is discarded. By always locking before signaling, you can
   
7.            (with care), avoid signaling before another thread has entered cond_wait().
   
8. 
   
9.            "cond_signal" will normally generate a warning if you attempt to use it on an unlocked variable. On the rare occasions where doing this
   
10.            may be sensible, you can suppress the warning with:
    
11. 
    
12.              { no warnings 'threads'; cond_signal($foo); }
    
13. 
    
14.        cond_broadcast VARIABLE
    
15.            The "cond_broadcast" function works similarly to "cond_signal".  "cond_broadcast", though, will unblock all the threads that are blocked
    
16.            in a "cond_wait" on the locked variable, rather than only one.
    

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always_waiting

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