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<title>Two-phase Termination 模式</title>
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<h3><a href="http://caterpillar.onlyfun.net/GossipCN/index.html">From
Gossip@caterpillar</a></h3>
<h1><a href="CppGossip.html">Design Pattern: Two-phase Termination 模式</a></h1>
Two-phase
Termination直譯的話是“兩相終止”，不過(guò)就這個(gè)模式而言，該譯作“兩階段終止”比較適當(dāng)，想像您有一個(gè)執(zhí)行緒正在周期性的運(yùn)作，在“運(yùn)作階
段”您送出了停止執(zhí)行緒的請(qǐng)求，這時(shí)候執(zhí)行緒不該慌張的馬上終止目前的工作，而是先完成這一次周期的工作，然后進(jìn)入“善后階段”完成一些善后的工作，例如
關(guān)閉檔案或網(wǎng)路串流，所謂的兩階段終止，即中止“運(yùn)作階段”，并完成“善后階段”，完整的完成執(zhí)行緒的工作。<br>
<br>
以Java的Thread終止而言，不建議您直接使用stop()方法來(lái)終止執(zhí)行緒，stop()方法會(huì)丟出ThreadDeath例外強(qiáng)迫執(zhí)行緒終止，即使執(zhí)行緒正在運(yùn)作階段或執(zhí)行至synchronized區(qū)，如果您要終止執(zhí)行緒，建議自行實(shí)作，例如：<br>
<div style="margin-left: 40px;"> <span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public class SomeThread extends Thread {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> private boolean isTerminated = false;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void terminate() {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> isTerminated = true;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void run() {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> while(!isTerminated) {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> // ... some statements</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br>
</div>
<br>
考慮到有時(shí)執(zhí)行緒可能會(huì)執(zhí)行至sleep()或wait()而進(jìn)入Not
Runnable狀態(tài)，使用上面的方法可能會(huì)延遲終止的請(qǐng)求，因而可以在要求終止時(shí)再呼叫interrupt()方法，這會(huì)丟出
InterruptedException，而使得執(zhí)行緒從Not Runnable狀態(tài)中離開(kāi)，因此可以改變一下程式：<br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public class SomeThread extends Thread {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> private boolean isTerminated = false;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
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