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JavaHL: Thread safety and Progress Notifications

From: Mark Phippard <markphip_at_gmail.com>
Date: 2007-11-26 15:37:32 CET

I have been getting some crashes lately in Subclipse (using 1.5
trunk). Kind of sporadic, not obvious recipe. I finally bothered to
take the time to look at the crash output (this is on OSX). I saw

Thread 22 Crashed:
0 libjvm.dylib 0x9bc16fb8 JVM_MonitorWait + 11444
1 libjvm.dylib 0x9bcd98bb JVM_IsInterrupted + 1797
2 libsvnjavahl-1.0.dylib 0x50cf8f6c
JNIEnv_::CallVoidMethod(_jobject*, _jmethodID*, ...) + 52 (jni.h:1034)
3 libsvnjavahl-1.0.dylib 0x50cde64d
ProgressListener::onProgress(long long, long long, apr_pool_t*) + 495
4 libsvnjavahl-1.0.dylib 0x50cde6c6
ProgressListener::progress(long long, long long, void*, apr_pool_t*) +
82 (ProgressListener.cpp:77)
5 libsvn_ra_neon-1.0.dylib 0x50c946f0 ra_neon_neonprogress + 99
6 libneon.26.dylib 0x515e2f0f ne_read_response_block + 145
7 libneon.26.dylib 0x515e33b5 ne_discard_response + 34
8 libneon.26.dylib 0x515e45aa ne_request_dispatch + 46
9 libsvn_ra_neon-1.0.dylib 0x50c98c18 svn_ra_neon__request_dispatch + 238
10 libsvn_ra_neon-1.0.dylib 0x50c98598 parsed_request + 577
11 libsvn_ra_neon-1.0.dylib 0x50c987ba svn_ra_neon__parsed_request + 114
12 libsvn_ra_neon-1.0.dylib 0x50c8a71c reporter_finish_report + 539
13 libsvn_client-1.0.dylib 0x512e3190 reporter_finish_report + 433
14 libsvn_wc-1.0.dylib 0x50ffeff0 svn_wc_crawl_revisions3 + 1613
15 libsvn_client-1.0.dylib 0x512e380a svn_client_status3 + 1605
16 libsvnjavahl-1.0.dylib 0x50ce74c5 SVNClient::status(char
const*, svn_depth_t, bool, bool, bool, bool, StatusCallback*) + 335
17 libsvnjavahl-1.0.dylib 0x50cef3b1
Java_org_tigris_subversion_javahl_SVNClient_status + 323

I think I know what the problem is. We recently started using the new
progress notifications. I think what happens is I take an option to
do an Update. We set the progress listener so that we can provide
feedback. At some point during this process, Eclipse kicks off a
status refresh in another thread (also normal). There is only one
JavaHL object. When the status operation starts, the progress
listener is still set because update is running. When update ends, it
is nulling out the progress listener.


Status goes to send a progress notification, and something is now null.

I have changed Subclipse so that we no longer null out the listener,
and instead just swallow the notifications that we do not want inside
our object. I wonder if there is some kind of safety checks that can
be added in the JavaHL C++ code though so that it does not crash. I
do not think what I am doing is that abnormal so someone else might
run into this.

Mark Phippard
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Received on Mon Nov 26 16:26:33 2007

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