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213516ef31
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.
249 lines
6.3 KiB
C++
249 lines
6.3 KiB
C++
/* Thread pool
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Copyright (C) 2019-2023 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "common-defs.h"
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#include "gdbsupport/thread-pool.h"
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#if CXX_STD_THREAD
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#include "gdbsupport/alt-stack.h"
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#include "gdbsupport/block-signals.h"
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#include <algorithm>
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#include <system_error>
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/* On the off chance that we have the pthread library on a Windows
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host, but std::thread is not using it, avoid calling
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pthread_setname_np on Windows. */
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#ifndef _WIN32
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#ifdef HAVE_PTHREAD_SETNAME_NP
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#define USE_PTHREAD_SETNAME_NP
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#endif
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#endif
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#ifdef USE_PTHREAD_SETNAME_NP
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#include <pthread.h>
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/* Handle platform discrepancies in pthread_setname_np: macOS uses a
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single-argument form, while Linux uses a two-argument form. NetBSD
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takes a printf-style format and an argument. This wrapper handles the
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difference. */
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ATTRIBUTE_UNUSED static void
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do_set_thread_name (int (*set_name) (pthread_t, const char *, void *),
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const char *name)
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{
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set_name (pthread_self (), "%s", const_cast<char *> (name));
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}
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ATTRIBUTE_UNUSED static void
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do_set_thread_name (int (*set_name) (pthread_t, const char *),
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const char *name)
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{
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set_name (pthread_self (), name);
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}
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/* The macOS man page says that pthread_setname_np returns "void", but
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the headers actually declare it returning "int". */
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ATTRIBUTE_UNUSED static void
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do_set_thread_name (int (*set_name) (const char *), const char *name)
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{
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set_name (name);
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}
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static void
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set_thread_name (const char *name)
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{
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do_set_thread_name (pthread_setname_np, name);
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}
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#elif defined (USE_WIN32API)
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#include <windows.h>
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typedef HRESULT WINAPI (SetThreadDescription_ftype) (HANDLE, PCWSTR);
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static SetThreadDescription_ftype *dyn_SetThreadDescription;
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static bool initialized;
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static void
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init_windows ()
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{
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initialized = true;
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HMODULE hm = LoadLibrary (TEXT ("kernel32.dll"));
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if (hm)
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dyn_SetThreadDescription
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= (SetThreadDescription_ftype *) GetProcAddress (hm,
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"SetThreadDescription");
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/* On some versions of Windows, this function is only available in
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KernelBase.dll, not kernel32.dll. */
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if (dyn_SetThreadDescription == nullptr)
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{
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hm = LoadLibrary (TEXT ("KernelBase.dll"));
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if (hm)
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dyn_SetThreadDescription
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= (SetThreadDescription_ftype *) GetProcAddress (hm,
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"SetThreadDescription");
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}
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}
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static void
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do_set_thread_name (const wchar_t *name)
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{
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if (!initialized)
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init_windows ();
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if (dyn_SetThreadDescription != nullptr)
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dyn_SetThreadDescription (GetCurrentThread (), name);
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}
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#define set_thread_name(NAME) do_set_thread_name (L ## NAME)
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#else /* USE_WIN32API */
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static void
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set_thread_name (const char *name)
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{
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}
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#endif
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#endif /* CXX_STD_THREAD */
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namespace gdb
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{
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/* The thread pool detach()s its threads, so that the threads will not
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prevent the process from exiting. However, it was discovered that
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if any detached threads were still waiting on a condition variable,
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then the condition variable's destructor would wait for the threads
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to exit -- defeating the purpose.
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Allocating the thread pool on the heap and simply "leaking" it
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avoids this problem.
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*/
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thread_pool *thread_pool::g_thread_pool = new thread_pool ();
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thread_pool::~thread_pool ()
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{
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/* Because this is a singleton, we don't need to clean up. The
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threads are detached so that they won't prevent process exit.
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And, cleaning up here would be actively harmful in at least one
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case -- see the comment by the definition of g_thread_pool. */
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}
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void
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thread_pool::set_thread_count (size_t num_threads)
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{
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#if CXX_STD_THREAD
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std::lock_guard<std::mutex> guard (m_tasks_mutex);
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/* If the new size is larger, start some new threads. */
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if (m_thread_count < num_threads)
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{
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/* Ensure that signals used by gdb are blocked in the new
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threads. */
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block_signals blocker;
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for (size_t i = m_thread_count; i < num_threads; ++i)
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{
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try
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{
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std::thread thread (&thread_pool::thread_function, this);
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thread.detach ();
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}
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catch (const std::system_error &)
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{
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/* libstdc++ may not implement std::thread, and will
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throw an exception on use. It seems fine to ignore
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this, and any other sort of startup failure here. */
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num_threads = i;
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break;
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}
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}
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}
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/* If the new size is smaller, terminate some existing threads. */
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if (num_threads < m_thread_count)
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{
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for (size_t i = num_threads; i < m_thread_count; ++i)
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m_tasks.emplace ();
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m_tasks_cv.notify_all ();
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}
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m_thread_count = num_threads;
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#else
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/* No threads available, simply ignore the request. */
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#endif /* CXX_STD_THREAD */
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}
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#if CXX_STD_THREAD
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void
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thread_pool::do_post_task (std::packaged_task<void ()> &&func)
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{
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std::packaged_task<void ()> t (std::move (func));
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if (m_thread_count != 0)
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{
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std::lock_guard<std::mutex> guard (m_tasks_mutex);
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m_tasks.emplace (std::move (t));
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m_tasks_cv.notify_one ();
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}
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else
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{
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/* Just execute it now. */
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t ();
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}
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}
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void
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thread_pool::thread_function ()
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{
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/* This must be done here, because on macOS one can only set the
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name of the current thread. */
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set_thread_name ("gdb worker");
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/* Ensure that SIGSEGV is delivered to an alternate signal
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stack. */
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gdb::alternate_signal_stack signal_stack;
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while (true)
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{
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optional<task_t> t;
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{
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/* We want to hold the lock while examining the task list, but
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not while invoking the task function. */
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std::unique_lock<std::mutex> guard (m_tasks_mutex);
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while (m_tasks.empty ())
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m_tasks_cv.wait (guard);
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t = std::move (m_tasks.front());
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m_tasks.pop ();
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}
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if (!t.has_value ())
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break;
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(*t) ();
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}
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}
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#endif /* CXX_STD_THREAD */
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} /* namespace gdb */
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