{"id":610,"date":"2010-01-25T13:30:10","date_gmt":"2010-01-25T17:30:10","guid":{"rendered":"http:\/\/benjamin.smedbergs.us\/blog\/?p=610"},"modified":"2010-01-25T13:30:10","modified_gmt":"2010-01-25T17:30:10","slug":"error-calling-method-on-npobject","status":"publish","type":"post","link":"http:\/\/benjamin.smedbergs.us\/blog\/2010-01-25\/error-calling-method-on-npobject\/","title":{"rendered":"Error calling method on NPObject!"},"content":{"rendered":"

When a plugin crashes, content script may still have a reference to JS objects provided by that plugin. The JS objects will throw an exception “Error calling method on NPObject” when any properties or methods are called. Unfortunately, this generic error message is also thrown whenever a plugin method fails for any reason. You can’t tell, just by looking at the exception, whether the process crashed or some other type of failure occurred.<\/p>\n

This is important when a test fails: there could be any number of different errors lurking under the surface with similar outward appearance. Today there was a Mochitest error<\/a> with the following symptoms:<\/p>\n

197 ERROR TEST-UNEXPECTED-FAIL | \/tests\/modules\/plugin\/test\/test_painting.html | [SimpleTest\/SimpleTest.js, window.onerror] An error occurred - Error calling method on NPObject! at http:\/\/localhost:8888\/tests\/modules\/plugin\/test\/test_painting.html:105\r\nPROCESS-CRASH | automation.py | application crashed (minidump found)\r\nThread 1 (crashed)\r\nPROCESS-CRASH | automation.py | application crashed (minidump found)\r\nThread 1 (crashed)\r\nPROCESS-CRASH | automation.py | application crashed (minidump found)\r\nThread 1 (crashed)\r\nPROCESS-CRASH | automation.py | application crashed (minidump found)\r\nThread 1 (crashed)<\/pre>\n
Reading through the log, however, the important output is:<\/p>\n
###!!! [RPCChannel][Child][\/builds\/moz2_slave\/mozilla-central-linux\/build\/ipc\/glue\/RPCChannel.cpp:276] Assertion (mDeferred.empty() || 1 == mDeferred.size()) failed.  expected mDeferred to have 0 or 1 items, but it has %lu (triggered by rpc)\r\n  local RPC stack size: 2863316886\r\n  remote RPC stack guess: 8\r\n  deferred stack size: 2863316886\r\n  out-of-turn RPC replies stack size: 2863316886\r\n  Pending queue size: 2863317142, front to back:<\/pre>\n
This assertion is immediately followed by an abort, which is visible in the crash dump output also:<\/p>\n
Crash reason:  SIGSEGV\r\nCrash address: 0xbdce4804\r\n\r\nThread 1 (crashed)\r\n 0  libxul.so!mozilla::ipc::RPCChannel::DebugAbort(char const*, int, char const*, char const*, char const*, bool) [ipc_message.h:0235fc257969 : 97 + 0x0]<\/pre>\n
David B. mistakenly thought that this was a manifestation of Bug 541102<\/a> when in fact it is an entirely unrelated bug with similar symptoms. When in doubt about a crash, please check with one of the Electrolysis team to help diagnose and read the log.<\/p>\n","protected":false},"excerpt":{"rendered":"
When a plugin crashes, content script may still have a reference to JS objects provided by that plugin. The JS objects will throw an exception “Error calling method on NPObject” when any properties or methods are called. Unfortunately, this generic error message is also thrown whenever a plugin method fails for any reason. You can’t […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[213,232],"class_list":["post-610","post","type-post","status-publish","format-standard","hentry","category-mozilla","tag-electrolysis","tag-oopp"],"_links":{"self":[{"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/posts\/610","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/comments?post=610"}],"version-history":[{"count":2,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/posts\/610\/revisions"}],"predecessor-version":[{"id":612,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/posts\/610\/revisions\/612"}],"wp:attachment":[{"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/media?parent=610"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/categories?post=610"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/benjamin.smedbergs.us\/blog\/wp-json\/wp\/v2\/tags?post=610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}