Q: I'm working on an application that uses both the
Thread Manager and the Network Services Library (NSL)
Manager. When the app quits, it crashes. What could be
causing this?
A: Once NSL is initialized either through
NSLOpenNavigationAPI or internally through a
call to NSLStandardGetURL, NSL and the SLP
plug-in start several threads for their own use. These
threads do not go away when
NSCloseNavigationAPI is called; instead, they wait
for the CFM termination routine to be invoked. The CFM
termination routines are called when the libraries are being
unloaded, which, for a standard application linked against
the NSL shared library NSLPPCLib, is after the application
has disposed all of its data and exited its main
function.
The issue arises if the application uses the Thread
Manager function SetThreadSwitcher to install
custom inner and outer context-switching functions on the
main thread. When the application is exiting it typically
disposes of all of its threads and any internal data
structures that refer to these threads. The main thread
still exists (it's still running), but the application's
internal references to it are gone.
After the app exits main the NSL/SLP
termination routine disposes of its threads. This causes the
app's outer context-switching function to be invoked for the
main thread. If this function assumes that its internal data
structure referring to this thread is still present, the
scene is set for a crash. Two possible workarounds are for
the application at exit time to:
- set the context-switching functions to
NULL or
- not dispose of any internal data structures used by
the outer context-switching function that refer to the
main thread.
An example of this issue can be found in the
PowerPlant framework from Metrowerks. The PowerPlant
LThread class installs inner and outer
context-switching functions on the main thread. When a
PowerPlant application exits, it disposes of all of its
threads and their respective LThread objects.
Then the NSL/SLP termination routine disposes of its
threads. This causes the app's main outer context-switching
function to be called and crash since its cover
LThread instance is already gone. There are two
PowerPlant fixes that can be applied:
- in
ExitThreads set the context-switching
functions to NULL
- in
ExitThreads do not dispose of the
main LThread.
This issue may be resolved in a future version of
NSL [2425291] but you will need to use one of these
workarounds on current systems.
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