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"
29 /* On the off chance that we have the pthread library on a Windows
30 host, but std::thread is not using it, avoid calling
31 pthread_setname_np on Windows. */
33 #ifdef HAVE_PTHREAD_SETNAME_NP
34 #define USE_PTHREAD_SETNAME_NP
38 #ifdef USE_PTHREAD_SETNAME_NP
42 /* Handle platform discrepancies in pthread_setname_np: macOS uses a
43 single-argument form, while Linux uses a two-argument form. This
44 wrapper handles the difference. */
46 ATTRIBUTE_UNUSED
static void
47 set_thread_name (int (*set_name
) (pthread_t
, const char *), const char *name
)
49 set_name (pthread_self (), name
);
52 ATTRIBUTE_UNUSED
static void
53 set_thread_name (void (*set_name
) (const char *), const char *name
)
58 #endif /* USE_PTHREAD_SETNAME_NP */
63 /* The thread pool detach()s its threads, so that the threads will not
64 prevent the process from exiting. However, it was discovered that
65 if any detached threads were still waiting on a condition variable,
66 then the condition variable's destructor would wait for the threads
67 to exit -- defeating the purpose.
69 Allocating the thread pool on the heap and simply "leaking" it
72 thread_pool
*thread_pool::g_thread_pool
= new thread_pool ();
74 thread_pool::~thread_pool ()
76 /* Because this is a singleton, we don't need to clean up. The
77 threads are detached so that they won't prevent process exit.
78 And, cleaning up here would be actively harmful in at least one
79 case -- see the comment by the definition of g_thread_pool. */
83 thread_pool::set_thread_count (size_t num_threads
)
85 std::lock_guard
<std::mutex
> guard (m_tasks_mutex
);
87 /* If the new size is larger, start some new threads. */
88 if (m_thread_count
< num_threads
)
90 /* Ensure that signals used by gdb are blocked in the new
92 block_signals blocker
;
93 for (size_t i
= m_thread_count
; i
< num_threads
; ++i
)
95 std::thread
thread (&thread_pool::thread_function
, this);
99 /* If the new size is smaller, terminate some existing threads. */
100 if (num_threads
< m_thread_count
)
102 for (size_t i
= num_threads
; i
< m_thread_count
; ++i
)
104 m_tasks_cv
.notify_all ();
107 m_thread_count
= num_threads
;
111 thread_pool::post_task (std::function
<void ()> func
)
113 std::packaged_task
<void ()> t (func
);
114 std::future
<void> f
= t
.get_future ();
116 if (m_thread_count
== 0)
118 /* Just execute it now. */
123 std::lock_guard
<std::mutex
> guard (m_tasks_mutex
);
124 m_tasks
.emplace (std::move (t
));
125 m_tasks_cv
.notify_one ();
131 thread_pool::thread_function ()
133 #ifdef USE_PTHREAD_SETNAME_NP
134 /* This must be done here, because on macOS one can only set the
135 name of the current thread. */
136 set_thread_name (pthread_setname_np
, "gdb worker");
139 /* Ensure that SIGSEGV is delivered to an alternate signal
141 gdb::alternate_signal_stack signal_stack
;
148 /* We want to hold the lock while examining the task list, but
149 not while invoking the task function. */
150 std::unique_lock
<std::mutex
> guard (m_tasks_mutex
);
151 while (m_tasks
.empty ())
152 m_tasks_cv
.wait (guard
);
153 t
= std::move (m_tasks
.front());
165 #endif /* CXX_STD_THREAD */