Ubuntu Manpage: include_server.py - conservative approximation of include dependencies for C/C++

NAME

       include_server.py - conservative approximation of include dependencies for C/C++

SYNOPSIS

       include_server --port INCLUDE_SERVER_PORT [OPTIONS]

DESCRIPTION

include_server.py starts an include server process. This process answers queries from distcc(1) clients
about what files to include in C/C++ compilations. The include_server.py command itself terminates as
soon as the include server has been spawned.

The INCLUDE_SERVER_PORT argument is the name of a socket used for all communication between distcc
clients and the include server. The distcc-pump(1) command is responsible for creating the socket
location, for passing it to this script, and for passing it to all distcc clients via the environment
variable named INCLUDE_SERVER_PORT.

The protocol used by the include server uses distcc's RPC implementation. Each distcc request consists of
(1) the current directory and (2) the list of arguments of the compilation command.

If the include server is able to process the request, then it answers the distcc client by sending a list
of filepaths. The filepaths are those of the compressed source and header files found to be necessary
for compilation through include analysis. The list also comprises symbolic links and even dummy files
needed for the compilation server to construct an accurate replica of the parts of the filesystem needed
for compilation. In this way, a needed header file like /path/foo.h is compressed, renamed, and stored
in a temporary location, such as /dev/shm/tmpiAvfGv.include_server-9368-1/path/foo.h.lzo. The distcc
client will pass these files on to a compilation server, where they will be uncompressed and mounted
temporarily.

If the include server is not able to process the request, then it returns the empty list to the distcc
client.

There are two kinds of failures that relate to the include server. The include server may fail to compute
the includes or fail in other ways, see section INCLUDE SERVER SYMPTOMS. Also, the compilation on the
remove server may fail due to inadequacy of the calculated include closure, but then succeed when locally
retried, see section DISTCC DISCREPANCY SYMPTOMS.

OPTION SUMMARY

The following options are understood by include_server.py.

-dPAT, --debug_pattern=PAT
Bit vector for turning on warnings and debugging
1 = warnings
2 = trace some functions
other powers of two: see include_server/basics.py.

-e, --email
Send email to 'distcc-pump-errors' or if defined, the value of enviroment variable
DISTCC_EMAILLOG_WHOM_TO_BLAME, when include server gets in trouble. The default is to not send
email.

--email_bound NUMBER
Maximal number of emails to send (in addition to a final email). Default: 3.

--no-email
Do not send email. This is the default.

--path_observation_re=RE
Issue warning message whenever a filename is resolved to a realpath that is matched by RE, which
is a regular expression in Python syntax. This is useful for finding out where files included
actually come from. Use RE="" to find them all. Note: warnings must be enabled with at least -d1.

--pid_file FILEPATH
The pid of the include server is written to file FILEPATH. This allows a script such a distcc-pump
to tear down the include server.

-s, --statistics
Print information to stdout about include analysis.

--stat_reset_triggers=LIST
Flush stat caches when the timestamp of any filepath in LIST changes or the filepath comes in or
out of existence. LIST is a colon separated string of filepaths, possibly containing simple globs
(as allowed by Python's glob module). Print a warning whenever such a change happens (if warnings
are enabled). This option allows limited exceptions to distcc-pump's normal assumption that source
files are not modified during the build.

-t, --time
Print elapsed, user, and system time to stderr.

--unsafe_absolute_includes
Do preprocessing on the compilation server even if includes of absolute filepaths are encountered.
Normally the include-server will fall back on local preprocessing if it detects any absolute
includes. Thus, this flag is useful for preventing such fallbacks when the absolute includes are
a false alarm, either because the absolute include is discarded during preprocessing or because
the absolutely included file exists on the compilation servers.

More precisely, with --unsafe_absolute_includes absolute includes are ignored for the purposes of
gathering the include closure. Using this option may lead to incorrect results because (1) the
header may actually be included on the compilation server and it may not be the same as on the
client, (2) the include directives of the header are not further analyzed.

The option is useful for compiling code that has such hardcoded absolute locations of header files
inside conditional directives (e.g. "#ifdef") that render the includes irrelevant. More
precisely, these includes must be eliminated during preprocessing for the actual configuration.
Then the question of existence of the header file is moot and the remote compilation is sound.
This is often the case if such includes are meant for unusual configurations different from the
actual configuration.

-v, --verify
Verify that files in CPP closure are contained in closure calculated by include processor.

-w, --write_include_closure
Write a .d_approx file which lists all the included files calculated by the include server; with
-x, additionally write the included files as calculated by CPP to a .d_exact file.

-x, --exact_analysis
Use CPP instead, do not omit system headers files.

INCLUDE SERVER SYMPTOMS AND ISSUES

The most likely messages and warnings to come from the include processor are listed below.

Preprocessing locally. Include server not covering: Couldn't determine default system include directories
To determine the default system header directories, the include server runs the compiler once for
each language needed during its session. This message indicates that the compiler specified to
distcc is not present on the client.

Preprocessing locally. Include server not covering: Bailing out because include server spent more than
...s user time handling request
In uncommon situations, the include server fails to analyze very complicated macro expressions.
The distcc client will use plain distcc mode.

Warning: Filepath must be relative but isn't
The include server does not accept absolute filepaths, such as /usr/include/stdio.h, in include
directives, because there is no guarantee that this header on the compilation server machine will
be the same as that on the client. The include server gives up analyzing the include closure. The
distcc client cannot use pump-mode.

To overcome this problem in a not always reliable way, set the environment variable
INCLUDE_SERVER_ARGS='--unsafe_absolute_includes' when invoking the distcc-pump script to pass the
--unsafe_absolute_includes option to the include server.

Warning: Absolute filepath ... was IGNORED
The --unsafe_absolute_includes is in use. This situation happens under the same circumstances as
when "Filepath must be relative but isn't" is issued, but in this case the include will provide an
answer to the distcc client.

Warning: Path '/PATH/FILE' changed/came into existence/no longer exists
These warnings are issued when using stat reset triggers. Because /PATH/FILE changed, the include
server clears its caches; the new version of the file (or the lack of it) renders the include
analysis invalid. This message can usually be ignored; it does signify a somewhat precarious use
of files by the build system. It is recommended to fix the build system so that files are not
rewritten.

Warning: For translation unit ..., lookup of file ... resolved to ... whose realpath is ...
This warning occurs with --path_observation_re when a new realpath matching a source or header
file is observed.

DISTCC DISCREPANCY SYMPTOMS

The interactions between the build system, distcc, and the include server is somewhat complex. When a
distcc commands receives a failing compilation from the remote server it retries the compilation locally.
This section discusses the causes of discrepancies between remote and local compilation. These are
flagged by the demotion message:

__________Warning: ... pump-mode compilation(s) failed on server, but succeeded locally.
__________Distcc-pump was demoted to plain mode. See the Distcc Discrepancy Symptoms section in the
include_server(1) man page.

The distcc-pump script issues this message at the end of the build. This means that for at least one
distcc invocation a local compilation succeeded after the remote compilation failed. Each distcc
invocation for which such a discrepancy occurred in turn also issues a message such as:

Warning: remote compilation of '...' failed, retried locally and got a different result.

The demotion makes subsequent distcc invocations use plain distcc mode. Thus preprocessing will take
place on the local machine for the remainder of the build. This technique prevents very slow builds
where all compilations end up on the local machine after failing remotely.

Of course, if the local compilations fails after the remote failures, then the distcc invocation exits
with the non-zero status of the local compilation. The error messages printed are also those of the local
compilation.

The fallback behavior for distcc-pump mode to local compilation can be disabled by setting the
environment variable DISTCC_FALLBACK to 1, which makes the distcc command fail as soon as the remote
compilation has failed. This setting is very useful for debugging why the remote compilation went wrong,
because now the output from the server will be printed.

Next we discuss the possible causes of discrepancies.

The user changed a source or header file during the build.
This yields inconsistent results of course.

A source or header file changed during the build.
The build system rewrites a file. For Linux kernel 2.6, this happens for
'include/linux/compile.h' and 'include/asm/asm-offsets.h'. This condition is fixed by letting the
include server know that it must reset its caches when a stat of any of the files changes.
Practically, this is done by gathering the files in a colon-separated list and then setting the
INCLUDE_SERVER_ARGS command as in:

include_server_args="--stat_reset_triggers=include/linux/compile.h:include/asm/asm-offsets.h"

A header file is potentially included, but does not exist, and is then later included.

This occurs when some header foo.h includes another header file trick.h, but the trick.h file has
not yet been generated and the inclusion is actually ignored because of preprocessing directives.
The include server will probe for the existence of trick.h, because it overapproximates all
possible ways directives actually evaluate. The file trick.h is determined not to exist. If it is
later generated, and then really included, then the include server will falsely believe that the
file still does not exist. The solution to this problem is to make the build system generate
trick.h before the first time any header file is included that makes a syntactic reference to
trick.h

The include server was started with --unsafe_absolute_includes.
This is a problem if there are header files locally that do not exist remotely and that are
actually used. Such includes are often protected by conditional directives that evaluate so that
are actually used on only specific and often uncommon platforms. If you are not compiling for such
a platform, then it may be correct to use --unsafe_absolute_include.

The include server has calculated the wrong includes.
We do not know of such a situation.

EXIT CODES

       The  exit  code  of  include_server.py is usually 0. That the include server has been started properly is
       communicated through the existence of the pid_file.

ENVIRONMENT VARIABLES

       DISTCC_EMAILLOG_WHOM_TO_BLAME The email address to use for include server automated emails.  The  default
       is 'distcc-pump-errors' (which is an email address that probably will not exist in your domain).

       Additionally, the invocation of the compiler may use additional environment variables.

BUGS

       If  you  think  you  have found a distcc bug, please see the file reporting-bugs.txt in the documentation
       directory for information on how to report it.

       In distcc-pump mode, the include server is unable to handle certain very complicated computed includes as
       found in parts of the Boost library. The include server will time out and distcc  will  revert  to  plain
       mode.

       Other known bugs may be documented on http://code.google.com/p/distcc/

AUTHOR

       The  include  server was written by Nils Klarlund, with assistance from Fergus Henderson, Manos Renieris,
       and Craig Silverstein. Please report bugs to <distcc@lists.samba.org>.

LICENCE

       You are free to use distcc.  distcc (including this manual) may be copied, modified or  distributed  only
       under  the  terms  of the GNU General Public Licence version 2 or later.  distcc comes with absolutely no
       warrany.  A copy of the GPL is included in the file COPYING.