3 Copyright (C) 2019 Free Software Foundation, Inc.
5 This file is part of GDB.
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
20 #include "common-defs.h"
24 #include "gdbsupport/thread-pool.h"
25 #include "gdbsupport/alt-stack.h"
26 #include "gdbsupport/block-signals.h"
28 #include "diagnostics.h"
30 /* On the off chance that we have the pthread library on a Windows
31 host, but std::thread is not using it, avoid calling
32 pthread_setname_np on Windows. */
34 #ifdef HAVE_PTHREAD_SETNAME_NP
35 #define USE_PTHREAD_SETNAME_NP
39 #ifdef USE_PTHREAD_SETNAME_NP
44 DIAGNOSTIC_IGNORE_UNUSED_FUNCTION
46 /* Handle platform discrepancies in pthread_setname_np: macOS uses a
47 single-argument form, while Linux uses a two-argument form. This
48 wrapper handles the difference. */
51 set_thread_name (int (*set_name
) (pthread_t
, const char *), const char *name
)
53 set_name (pthread_self (), name
);
57 set_thread_name (void (*set_name
) (const char *), const char *name
)
64 #endif /* USE_PTHREAD_SETNAME_NP */
69 /* The thread pool detach()s its threads, so that the threads will not
70 prevent the process from exiting. However, it was discovered that
71 if any detached threads were still waiting on a condition variable,
72 then the condition variable's destructor would wait for the threads
73 to exit -- defeating the purpose.
75 Allocating the thread pool on the heap and simply "leaking" it
78 thread_pool
*thread_pool::g_thread_pool
= new thread_pool ();
80 thread_pool::~thread_pool ()
82 /* Because this is a singleton, we don't need to clean up. The
83 threads are detached so that they won't prevent process exit.
84 And, cleaning up here would be actively harmful in at least one
85 case -- see the comment by the definition of g_thread_pool. */
89 thread_pool::set_thread_count (size_t num_threads
)
91 std::lock_guard
<std::mutex
> guard (m_tasks_mutex
);
93 /* If the new size is larger, start some new threads. */
94 if (m_thread_count
< num_threads
)
96 /* Ensure that signals used by gdb are blocked in the new
98 block_signals blocker
;
99 for (size_t i
= m_thread_count
; i
< num_threads
; ++i
)
101 std::thread
thread (&thread_pool::thread_function
, this);
105 /* If the new size is smaller, terminate some existing threads. */
106 if (num_threads
< m_thread_count
)
108 for (size_t i
= num_threads
; i
< m_thread_count
; ++i
)
110 m_tasks_cv
.notify_all ();
113 m_thread_count
= num_threads
;
117 thread_pool::post_task (std::function
<void ()> func
)
119 std::packaged_task
<void ()> t (func
);
120 std::future
<void> f
= t
.get_future ();
122 if (m_thread_count
== 0)
124 /* Just execute it now. */
129 std::lock_guard
<std::mutex
> guard (m_tasks_mutex
);
130 m_tasks
.emplace (std::move (t
));
131 m_tasks_cv
.notify_one ();
137 thread_pool::thread_function ()
139 #ifdef USE_PTHREAD_SETNAME_NP
140 /* This must be done here, because on macOS one can only set the
141 name of the current thread. */
142 set_thread_name (pthread_setname_np
, "gdb worker");
145 /* Ensure that SIGSEGV is delivered to an alternate signal
147 gdb::alternate_signal_stack signal_stack
;
154 /* We want to hold the lock while examining the task list, but
155 not while invoking the task function. */
156 std::unique_lock
<std::mutex
> guard (m_tasks_mutex
);
157 while (m_tasks
.empty ())
158 m_tasks_cv
.wait (guard
);
159 t
= std::move (m_tasks
.front());
171 #endif /* CXX_STD_THREAD */