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ios: Life of a crash report documentation.

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Bug: crashpad: 31
Change-Id: Ic67aa0450cc273bd4088c494ed2656365b700198
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/3234451
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
This commit is contained in:
Justin Cohen 2021-10-28 17:08:41 -04:00 committed by Crashpad LUCI CQ
parent fad3bdcde0
commit d842c3c4c6
2 changed files with 74 additions and 1 deletions
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2
client/crashpad_client_ios.cc
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@ -75,6 +75,7 @@ class CrashHandler : public Thread,
LOG(ERROR) << "Unable to initialize Crashpad.";
return false;
}
InstallObjcExceptionPreprocessor(this);
INITIALIZATION_STATE_SET_VALID(initialized_);
return true;
}
@ -312,7 +313,6 @@ bool CrashpadClient::StartCrashpadInProcessHandler(
const std::map<std::string, std::string>& annotations) {
CrashHandler* crash_handler = CrashHandler::Get();
DCHECK(crash_handler);
InstallObjcExceptionPreprocessor(crash_handler);
return crash_handler->Initialize(database, url, annotations);
}

73
doc/ios_overview_design.md
View File

@ -69,6 +69,71 @@ arrays.
Similar to JSON, maps can contain other maps, arrays and properties.
## The life of an iOS crash report
Immediately upon calling StartCrashpadInProcessHandler, the iOS in-process
handler is installed. This will open a temporary file within the database
directory, in a subdirectory named `pending-serialized-ios-dump`. This file will
be used to write an intermediate dump in the event of a crash. This must happen
before installing the various types of crash handlers, as each depends on having
a valid handler with an intermediate dump ready to be written to.
After the in-process handler is initialized, the Mach exception, POSIX signal
and Objective-C exception preprocessor handlers are installed.
### Intermediate Dump File Locking
It is expected that multiple Crashpad clients may share the same database
directory, and this directory may be inside an iOS app group directory. While
it's possible for each Crashpad client to write to its own private directory,
if a shared directory is used, it's possible for different applications to
upload a crash report from any application in a shared group. This might be
used, for example, by an application and its various app extensions, where each
client may generate a crash report but only the main application uploads
reports. Alternatively, a suite of applications may upload each other's crash
reports. Otherwise, the only opportunity to upload a report would be when a
specific app that crashed relaunches.
To prevent multiple clients from processing a pending intermediate dump, files
must be locked. However, POSIX locks on app group files will trigger app
termination on app backgrounding, so a custom file locking protocol is used.
Locked temporary files are named `<bundle-id>@<uuid>.locked`. The `.locked`
extension is removed when the file is unlocked. The `bundle-id` is used to
determine which Crashpad clients can process leftover locked files.
### Writing Crashes to Intermediate Dumps
When an app encounters a crash (via a Mach exception, Objective-C exception, or
a POSIX signal), an intermediate dump is written to the temporary locked file,
the .locked extension is removed, and a new temporary locked file is opened.
App terminations not handled by Crashpad will leave behind a temporary
locked file, to be cleaned up on next launch. These files are still processed,
because it is possible for the app to be terminated while writing an
intermediate dump, and if enough data is written this may still be valuable.
Note: Generally iOS apps are single-process, so it's safe for the client to
consider any files matching its `bundle-id`, but there are edge-cases (such as
if a share-to app extension is opened at the same time in two different apps) so
old locked files won't be cleared until after 24 hours. Any locked file found
after 60 days is unlocked regardless of `bundle-id`.
### Writing to Intermediate Dumps without a Crash
Apps may also generate intermediate dumps without a crash, often used for
debugging. Chromium makes heavy use of this for detecting main thread hangs,
something that can appear as a crash for the user, but is uncatchable for crash
handlers like Crashpad. When an app requests this (via DumpWithoutCrash,
DumpWithoutCrashAndDeferProcessing), an intermediate dump is written to the
temporary locked file, the .locked extension is removed, and a new temporary
locked file is opened.
Note: DumpWithoutCrashAndDeferProcessingAtPath writes an intermediate dump to
the requested location, not the previously opened temporary file. This is useful
because Chromium's main thread hang detection will throw away hang reports in
certain circumstances (if the app recovers, if a different crash report is
written, etc).
## The Crashpad In-Process Client
Other Crashpad platforms handle exceptions and upload minidumps out-of-process.
@ -81,6 +146,11 @@ intermediate dumps into pending minidumps and begin processing pending
minidumps, possibly for upload, at suitable times following the next application
restart.
Note: Applications are not required to call either of these methods. For
example, application extensions may choose to generate dumps but leave
processing and uploading to the main applications. Clients that share the
same database directory between apps can take advantage of processing and
uploading crash reports from different applications.
### `ProcessIntermediateDumps`
For performance and stability reasons applications may choose the correct time
@ -96,6 +166,9 @@ the next call to `ProcessIntermediateDumps`. Conversely,
stability concerns. In this case, intermediate dumps are automatically
converted to minidumps and immediately eligible for uploading.
Applications can include annotations here as well. Chromium uses this for its
insta-crash logic, which detects if an app is crashing repeatedly on startup.
### `StartProcessingPendingReports`
For similar reasons, applications may choose the correct time to begin uploading
pending reports, such as when ideal network conditions exist. By default,