From the python docs: "In general, the key and reverse conversion processes
are much faster than specifying an equivalent cmp function. This is because
cmp is called multiple times for each list element while key and reverse touch
each element only once."
To achieve this, the "direct prerequisites" for a File node are stored in the
node's attributes object, instead of in the build environment for the node.
This allows the emitter for nodes to amend _other nodes_ prerequisites. After that,
this change is trivial. Introduce a LIBDEPS_DEPENDENTS environment variable that sets
the named dependents of a node, while the existing LIBDEPS variable may be considered
the direct prerequisites.
The previous implementation was not recursively following the LIBDEPS hierarchy, looking for SYSLIBDEPS
to add. Instead, it was trying to walk a hierachy like LIBDEPS rooted in the SYSLIBDEPS variable. This
isn't really a meaningful behavior, since SYSLIBDEPS always list system libraries, which are always leaf
nodes in the dependency graph for our build system.
SCons (correctly) considers two link command lines different if the order of
object files or static libraries changes. As a result, the libdeps system needs
to produce consistent ordering of these files in the $_LIBDEPS expansion. This
patch achieves this by sorting the _LIBDEPS candidate expansion by the string
name of the expanded objects.
This problem is akin to that from SERVER-5254, which was solved in a similar
manner.
Turns out that SCons.Node objects are compared on object identity (pointer),
not some value that's stable across invocations of SCons. We now sort by
the "name" of the node (its string representation), instead, which stops
spurious builds.
This is used to fix linking of programs on Windows that depend on static
initializer execution in object files that don't contain symbols referenced
directly by the program at compile time (i.e., Command registration).
It also unifies the compilation of these sorts of programs on Windows and POSIX
systems, eliminating the use of a MergeLibrary when linking mongod and mongos.
This extension to libdeps could also be used to reimagine MergeLibrary to have
an implementation shared between Posix and Windows systems. The existing
MergeLibrary system uses relocatable objects on Posix systems, and thus could
behave differently from the one on Windows, with respect to the exeuction of
static initializers. That change is recommended future work.
Newer versions of SCons are more consistent about making lists out of TARGET and
SOURCE fields than older (1.2.0 and older) versions. This patch bandaids that
problem, which was exposed by the libdeps module.
This patch is a reorganization of our build files, which brings them slightly
closer in line with standard SCons organization.
In particular, the SConstruct file sets up the various "build environment"
objects, by examining the local system and command line parameters. Then, it
delegates to some SConscript files, which describe build rules, like how to
compile "mongod" from source.
Typically, you would create several SConscript files for a project this large,
after breaking the project into logical sub projects, such as "platform
abstraction", "data manager", "query optimizer", etc. That will be future work.
For now, we only separate out the special rules for executing smoke tests into
SConscript.smoke. Pretty much all other build rules are in src/mongo/SConscript.
"tools" are placed in site_scons/site_tools.
This patch also includes better support for building and tracking dependencies
among static libraries ("libdeps" and "MergeLibrary"), and some incumbent, minor
restructuring.
This patch introduces a "warning" message from SCons about framework.o having
two rules that generate it. It is harmless, for now, and will be removed in
future work.
Future work also includes eliminating use of the SCons "Glob" utility, and
restructuring the source code into sensible components.
