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This commit enables the early initialization commands (92e4e97a9f5) to
modify the number of threads used by gdb's thread pool.
The motivation here is to prevent gdb from spawning a detrimental number
of threads on many-core systems under environments with restrictive
ulimits.
With gdb before this commit, the thread pool takes the following sizes:
1. Thread pool size is initialized to 0.
2. After the maintenance commands are defined, the thread pool size is
set to the number of system cores (if it has not already been set).
3. Using early initialization commands, the thread pool size can be
changed using "maint set worker-threads".
4. After the first prompt, the thread pool size can be changed as in the
previous step.
Therefore after step 2. gdb has potentially launched hundreds of threads
on a many-core system.
After this change, step 2 and 3 are reversed so there is an opportunity
to set the required number of threads without needing to default to the
number of system cores first.
There does exist a configure option (added in 261b07488b9) to disable
multithreading, but this does not allow for an already deployed gdb to
be configured.
Additionally, the default number of worker threads is clamped at eight
to control the number of worker threads spawned on many-core systems.
This value was chosen as testing recorded on bugzilla issue 29959
indicates that parallel efficiency drops past this point.
GDB built with GCC 13.
No test suite regressions detected. Compilers: GCC, ACfL, Intel, Intel
LLVM, NVHPC; Platforms: x86_64, aarch64.
The scenario that interests me the most involves preventing GDB from
spawning any worker threads at all. This was tested by counting the
number of clones observed by strace:
strace -e clone,clone3 gdb/gdb -q \
--early-init-eval-command="maint set worker-threads 0" \
-ex q ./gdb/gdb |& grep --count clone
The new test relies on "gdb: install CLI uiout while processing early
init files" developed by Andrew Burgess. This patch will need pushing
prior to this change.
The clamping was tested on machines with both 16 cores and a single
core. "maint show worker-threads" correctly reported eight and one
respectively.
Approved-By: Tom Tromey <tom@tromey.com>
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Since GDB now requires C++17, we don't need the internally maintained
gdb::optional implementation. This patch does the following replacing:
- gdb::optional -> std::optional
- gdb::in_place -> std::in_place
- #include "gdbsupport/gdb_optional.h" -> #include <optional>
This change has mostly been done automatically. One exception is
gdbsupport/thread-pool.* which did not use the gdb:: prefix as it
already lives in the gdb namespace.
Change-Id: I19a92fa03e89637bab136c72e34fd351524f65e9
Approved-By: Tom Tromey <tom@tromey.com>
Approved-By: Pedro Alves <pedro@palves.net>
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This commit is the result of running the gdb/copyright.py script,
which automated the update of the copyright year range for all
source files managed by the GDB project to be updated to include
year 2023.
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PR build/29110 points out that GDB fails to build on mingw when the
"win32" thread model is in use. It turns out that the Fedora cross
tools using the "posix" thread model, which somehow manages to support
std::future, whereas the win32 model does not.
While looking into this, I found that the configuring with
--disable-threading will also cause a build failure.
This patch fixes this build by introducing a compatibility wrapper for
std::future.
I am not able to test the win32 thread model build, but I'm going to
ask the reporter to try this patch.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29110
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This patch is a bit different from the rest of the series, in that it
is a change to gdb's behavior on the host. It changes gdb's thread
pool to try to set the thread name on Windows, if SetThreadDescription
is available.
This is part of PR win32/29050.
This patch isn't likely to be useful to many people in the short term,
because the Windows port of the libstdc++ thread code is not upstream.
(AdaCore uses it, and sent it upstream, but it did not land, I don't
know why.) However, if that patch does ever go in, or presumably if
you build using some other C++ runtime library, then this will be
useful.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29050
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When I build gdb with gcc 8.3, there exist the following build errors,
rename the typedef to task_t to fix them.
CXX thread-pool.o
In file included from /home/loongson/gdb.git/gdbsupport/thread-pool.cc:21:
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h: In member function ‘std::future<void> gdb::thread_pool::post_task(std::function<void()>&&)’:
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h:69:44: error: declaration of ‘task’ shadows a previous local [-Werror=shadow=local]
std::packaged_task<void ()> task (std::move (func));
^~~~
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h:102:39: note: shadowed declaration is here
typedef std::packaged_task<void ()> task;
^~~~
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h: In member function ‘std::future<_Res> gdb::thread_pool::post_task(std::function<T()>&&)’:
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h:80:41: error: declaration of ‘task’ shadows a previous local [-Werror=shadow=local]
std::packaged_task<T ()> task (std::move (func));
^~~~
/home/loongson/gdb.git/gdbsupport/../gdbsupport/thread-pool.h:102:39: note: shadowed declaration is here
typedef std::packaged_task<void ()> task;
^~~~
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
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This changes gdb::parallel_for_each to return a vector of the results.
However, if the passed-in function returns void, the return type
remains 'void'. This functionality is used later, to parallelize the
new indexer.
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thread-pool.h requires CXX_STD_THREAD in order to even be included.
However, there's no deep reason for this, and during review we found
that one patch in the new DWARF indexer series unconditionally
requires the thread pool.
Because the thread pool already allows a task to be run in the calling
thread (for example if it is configured to have no threads in the
pool), it seemed straightforward to make this code ok to use when host
threads aren't available at all.
This patch implements this idea. I built it on a thread-less host
(mingw, before my recent configure patch) and verified that the result
builds.
After the thread-pool change, parallel-for.h no longer needs any
CXX_STD_THREAD checks at all, so this patch removes these as well.
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This commit brings all the changes made by running gdb/copyright.py
as per GDB's Start of New Year Procedure.
For the avoidance of doubt, all changes in this commits were
performed by the script.
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Tankut's recent patches made me realize that thread_pool::post_task
should have used an rvalue reference for its parameter. This patch
makes this change.
gdbsupport/ChangeLog
2021-04-30 Tom Tromey <tromey@adacore.com>
* thread-pool.cc (thread_pool::post_task): Update.
* thread-pool.h (class thread_pool) <post_task>: Take rvalue
reference to function.
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This commits the result of running gdb/copyright.py as per our Start
of New Year procedure...
gdb/ChangeLog
Update copyright year range in copyright header of all GDB files.
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libstdc++ might change so that it always implements std::thread, but
then have thread startup simply fail. This is being discussed here:
https://gcc.gnu.org/pipermail/gcc-patches/2020-November/558736.html
This patch pre-emptively changes gdb to handle this scenario. It
seemed fine to me to ignore all system errors at thread startup, so
that is what this does.
gdbsupport/ChangeLog
2020-11-20 Tom Tromey <tromey@adacore.com>
* thread-pool.cc (thread_pool::set_thread_count): Ignore system
errors.
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This patch renames the .c source files in gdbsupport to .cc.
In the gdb directory, there is an argument against renaming the source
files, which is that it makes using some git commands more difficult to
do archeology. Some commands have some kind of "follow" option that
makes git try to follow renames, but it doesn't work in all situations.
Given that we have just moved the gdbsupport directory, that argument
doesn't hold for source files in that directory. I therefore suggest
renaming them to .cc, so that they are automatically recognized as C++
by various tools and editors.
The original motivation behind this is that when building gdbsupport
with clang, I get:
CC agent.o
clang: error: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Werror,-Wdeprecated]
In the gdb/ directory, we make clang happy by passing "-x c++". We
could do this in gdbsupport too, but I think that renaming the files is
a better long-term solution.
gdbserver still does its own build of gdbsupport, so a few changes in
its Makefile are necessary.
gdbsupport/ChangeLog:
* Makefile.am: Rename source files from .c to .cc.
(CC, CFLAGS): Don't override.
(AM_CFLAGS): Rename to ...
(AM_CXXFLAGS): ... this.
* Makefile.in: Re-generate.
* %.c: Rename to %.cc.
gdbserver/ChangeLog:
* Makefile.in: Rename gdbsupport source files from .c to .cc.
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