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POPossibility for deadlock to occur during IPC call
 

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  1. POPossibility for deadlock to occur during IPC call
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    <p>I have a <code>MainActivity</code> which will issue IPC call to a remote <code>AutoCompleteService</code> service. </p> <p>During execution of <code>AutoCompleteService</code>'s IPC function, the service will issue another IPC call back to <code>MainActivity</code>.</p> <h2>MainActivity.java</h2> <pre><code>// Receive IPC call from AutoCompleteService. private StockInfoObserver.Stub stockInfoObserver = new StockInfoObserver.Stub() { @Override public void update(StockInfo stockInfo) throws RemoteException { // TODO Auto-generated method stub Log.i(TAG, android.os.Process.myPid() + " : MainActivity receive ipc call : " + Thread.currentThread().getId()); } }; ... ... ... // Issue IPC call to AutoCompleteService. button.setOnClickListener(new OnClickListener() { @Override public void onClick(View arg0) { // Test on API. try { Log.i(TAG, android.os.Process.myPid() + " : MainActivity start issue IPC call to remote service : " + Thread.currentThread().getId()); // autoCompleteApi.handle will issue IPC call to remote service. autoCompleteApi.handle("abc"); Log.i(TAG, android.os.Process.myPid() + " : MainActivity end issue IPC call to remote service : " + Thread.currentThread().getId()); } catch (RemoteException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }); </code></pre> <h2>AutoCompleteService.java</h2> <pre><code>private AutoCompleteApi.Stub autoCompleteApi = new AutoCompleteApi.Stub() { private List&lt;StockInfoObserver&gt; stockInfoObservers = new ArrayList&lt;StockInfoObserver&gt;(); @Override public void handle(String string) { Log.i(TAG, android.os.Process.myPid() + " : AutoCompleteService start receive ipc call : " + Thread.currentThread().getId()); try { for (StockInfoObserver stockInfoObserver : stockInfoObservers) { Log.i(TAG, android.os.Process.myPid() + " : AutoCompleteService start IPC call to MainActivity : " + Thread.currentThread().getId()); // stockInfoObserver.update will issue IPC call back to MainActivity stockInfoObserver.update(null); Log.i(TAG, android.os.Process.myPid() + " : AutoCompleteService end IPC call to MainActivity : " + Thread.currentThread().getId()); } } catch (RemoteException e) { // TODO Auto-generated catch block e.printStackTrace(); } Log.i(TAG, android.os.Process.myPid() + " : AutoCompleteService end receive ipc call : " + Thread.currentThread().getId()); } @Override public void attachStockInfoObserver(StockInfoObserver stockInfoObserver) throws RemoteException { if (stockInfoObservers.contains(stockInfoObserver) == false) { stockInfoObservers.add(stockInfoObserver); } } }; </code></pre> <p>My initial expectation is that, <strong>deadlock will occur</strong>. This is due to my observation. When issuing an IPC call, the issuer will only return from IPC call, after the IPC receiver finished its IPC function execution.</p> <ol> <li><code>MainActivity</code> issues IPC call to <code>AutoCompleteService</code> through <code>autoCompleteApi.handle</code>.</li> <li><code>MainActivity</code> will now wait till <code>AutoCompleteService</code> finished its execution.</li> <li><code>AutoCompleteService</code> issues IPC call to <code>MainActivity</code> through <code>stockInfoObserver.update</code>.</li> <li><code>AutoCompleteService</code> will now wait till <code>MainActivity</code> finished its execution.</li> <li>However, <code>MainActivity</code>'s thread is still waiting, there are no thread which will perform <code>update</code> function.</li> <li>Both processes keep waiting for each others.</li> </ol> <p>However, the above doesn't occur. This is the Log I'm getting. Everything just work flawless.</p> <pre><code>// Log in MainActivity TAG 3930 : MainActivity start issue IPC call to remote service : 1 3930 : MainActivity receive ipc call : 1 3930 : MainActivity end issue IPC call to remote service : 1 </code></pre> <hr> <pre><code>// Log in AutoCompleteService TAG 3961 : AutoCompleteService start receive ipc call : 494 3961 : AutoCompleteService start IPC call to MainActivity : 494 3961 : AutoCompleteService end IPC call to MainActivity : 494 3961 : AutoCompleteService end receive ipc call : 494 </code></pre> <hr> <p>But I don't really understand. <strong>If the MainActivity thread (with Id 1) is not returning from a function call (<code>autoCompleteApi.handle</code>), how can it "jump" over to execute another function (<code>update(StockInfo stockInfo)</code>)?</strong></p> <p>I would be expecting <strong>MainActivity receive ipc call</strong> being printed by different thread. Not the thread with Id 1. If not, deadlock should occur.</p> <p>In case you are interested to try to out, kindly download the complete source code right here : <a href="https://www.dropbox.com/s/8hd7v5acjd213l1/jstock-android2.zip" rel="nofollow">https://www.dropbox.com/s/8hd7v5acjd213l1/jstock-android2.zip</a></p>
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    1. PO
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    1. PTQuestion
    1. USCheok Yan Cheng
    1. USCheok Yan Cheng
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      1. POPossibility for deadlock to occur during IPC call
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      1. VTUpMod
    2. VO
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      1. POPossibility for deadlock to occur during IPC call
      1. USHenry
      1. VTFavorite
    1. COMy guess would be that LogCat can't keep up with process change here. It really makes no sense you receive IPC callback back to MainActivity before logs from AutoCompleteService are written.
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      1. POPossibility for deadlock to occur during IPC call
      1. USharism
    2. COSorry. The log are from 2 different TAG.
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      1. POPossibility for deadlock to occur during IPC call
      1. USCheok Yan Cheng
 

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