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Diffstat (limited to 'gdbsupport/thread-pool.c')
| -rw-r--r-- | gdbsupport/thread-pool.c | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/gdbsupport/thread-pool.c b/gdbsupport/thread-pool.c new file mode 100644 index 00000000000..fc83ff765f6 --- /dev/null +++ b/gdbsupport/thread-pool.c @@ -0,0 +1,167 @@ +/* Thread pool + + Copyright (C) 2019-2020 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#include "common-defs.h" + +#if CXX_STD_THREAD + +#include "gdbsupport/thread-pool.h" +#include "gdbsupport/alt-stack.h" +#include "gdbsupport/block-signals.h" +#include <algorithm> + +/* On the off chance that we have the pthread library on a Windows + host, but std::thread is not using it, avoid calling + pthread_setname_np on Windows. */ +#ifndef _WIN32 +#ifdef HAVE_PTHREAD_SETNAME_NP +#define USE_PTHREAD_SETNAME_NP +#endif +#endif + +#ifdef USE_PTHREAD_SETNAME_NP + +#include <pthread.h> + +/* Handle platform discrepancies in pthread_setname_np: macOS uses a + single-argument form, while Linux uses a two-argument form. This + wrapper handles the difference. */ + +ATTRIBUTE_UNUSED static void +set_thread_name (int (*set_name) (pthread_t, const char *), const char *name) +{ + set_name (pthread_self (), name); +} + +/* The macOS man page says that pthread_setname_np returns "void", but + the headers actually declare it returning "int". */ +ATTRIBUTE_UNUSED static void +set_thread_name (int (*set_name) (const char *), const char *name) +{ + set_name (name); +} + +#endif /* USE_PTHREAD_SETNAME_NP */ + +namespace gdb +{ + +/* The thread pool detach()s its threads, so that the threads will not + prevent the process from exiting. However, it was discovered that + if any detached threads were still waiting on a condition variable, + then the condition variable's destructor would wait for the threads + to exit -- defeating the purpose. + + Allocating the thread pool on the heap and simply "leaking" it + avoids this problem. +*/ +thread_pool *thread_pool::g_thread_pool = new thread_pool (); + +thread_pool::~thread_pool () +{ + /* Because this is a singleton, we don't need to clean up. The + threads are detached so that they won't prevent process exit. + And, cleaning up here would be actively harmful in at least one + case -- see the comment by the definition of g_thread_pool. */ +} + +void +thread_pool::set_thread_count (size_t num_threads) +{ + std::lock_guard<std::mutex> guard (m_tasks_mutex); + + /* If the new size is larger, start some new threads. */ + if (m_thread_count < num_threads) + { + /* Ensure that signals used by gdb are blocked in the new + threads. */ + block_signals blocker; + for (size_t i = m_thread_count; i < num_threads; ++i) + { + std::thread thread (&thread_pool::thread_function, this); + thread.detach (); + } + } + /* If the new size is smaller, terminate some existing threads. */ + if (num_threads < m_thread_count) + { + for (size_t i = num_threads; i < m_thread_count; ++i) + m_tasks.emplace (); + m_tasks_cv.notify_all (); + } + + m_thread_count = num_threads; +} + +std::future<void> +thread_pool::post_task (std::function<void ()> func) +{ + std::packaged_task<void ()> t (func); + std::future<void> f = t.get_future (); + + if (m_thread_count == 0) + { + /* Just execute it now. */ + t (); + } + else + { + std::lock_guard<std::mutex> guard (m_tasks_mutex); + m_tasks.emplace (std::move (t)); + m_tasks_cv.notify_one (); + } + return f; +} + +void +thread_pool::thread_function () +{ +#ifdef USE_PTHREAD_SETNAME_NP + /* This must be done here, because on macOS one can only set the + name of the current thread. */ + set_thread_name (pthread_setname_np, "gdb worker"); +#endif + + /* Ensure that SIGSEGV is delivered to an alternate signal + stack. */ + gdb::alternate_signal_stack signal_stack; + + while (true) + { + optional<task> t; + + { + /* We want to hold the lock while examining the task list, but + not while invoking the task function. */ + std::unique_lock<std::mutex> guard (m_tasks_mutex); + while (m_tasks.empty ()) + m_tasks_cv.wait (guard); + t = std::move (m_tasks.front()); + m_tasks.pop (); + } + + if (!t.has_value ()) + break; + (*t) (); + } +} + +} + +#endif /* CXX_STD_THREAD */ |