hpcrun: Integrate libmonitor
libmonitor is a library hpcrun uses to intercept important moments such as program start, thread creation, signal handling, etc. Unfortunately having libmonitor as a separate library will not be compatible with various low-level improvements to hpcrun, in particular #706 and #791. The rational solution is to integrate libmonitor into the hpcrun codebase first.
Current Issues / Rationale
libmonitor is a library that, when LD_PRELOAD'd, allows a client library (e.g. hpcrun) to capture and intercept important moments of the application execution, such as program start and thread creation. It also handles tracking threads that are hung and shooting them down with signals at program termination if needed, among other features. However, hpcrun requires far more than libmonitor itself provides, leading to duplicated symbol wrapping tech in the hpcrun codebase as well as extensions to the libmonitor API to (hackily) ignore some threads (at various points) or add wrappers for certain signals. In addition, hpcrun's own signal code is semi-incompatible with that in libmonitor, meaning HPCToolkit is only compatible with a customized build of libmonitor instead of a stock build. In practice, this leads to pointlessly tangled and underdesigned APIs between the shared libraries in question.
Doing this also prevents a number of semi-internal symbols from being exposed to the application, lowering the potential for application breakage and improving our overall cleanliness.
Proposed Solution
The libmonitor source should be copied into the src/tool/hpcrun directory and its source files linked into libhpcrun* as appropriate. Any customizations required should be applied directly to the copied source code, the hpcrun and hpclink wrapper scripts should no longer do anything with libmonitor, and the top-level --with-libmonitor dependency should be dropped.
Affected Code Paths
- Build system
configure.acsrc/tool/hpcrun/Makefile.am