1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
/* Thread pool
Copyright (C) 2019-2022 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"
#include "gdbsupport/thread-pool.h"
#if CXX_STD_THREAD
#include "gdbsupport/alt-stack.h"
#include "gdbsupport/block-signals.h"
#include <algorithm>
#include <system_error>
/* 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. NetBSD
takes a printf-style format and an argument. This wrapper handles the
difference. */
ATTRIBUTE_UNUSED static void
set_thread_name (int (*set_name) (pthread_t, const char *, void *),
const char *name)
{
set_name (pthread_self (), "%s", const_cast<char *> (name));
}
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 */
#endif /* CXX_STD_THREAD */
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)
{
#if CXX_STD_THREAD
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)
{
try
{
std::thread thread (&thread_pool::thread_function, this);
thread.detach ();
}
catch (const std::system_error &)
{
/* libstdc++ may not implement std::thread, and will
throw an exception on use. It seems fine to ignore
this, and any other sort of startup failure here. */
num_threads = i;
break;
}
}
}
/* 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;
#else
/* No threads available, simply ignore the request. */
#endif /* CXX_STD_THREAD */
}
std::future<void>
thread_pool::post_task (std::function<void ()> &&func)
{
std::packaged_task<void ()> t (std::move (func));
std::future<void> f = t.get_future ();
#if CXX_STD_THREAD
if (m_thread_count != 0)
{
std::lock_guard<std::mutex> guard (m_tasks_mutex);
m_tasks.emplace (std::move (t));
m_tasks_cv.notify_one ();
}
else
#endif
{
/* Just execute it now. */
t ();
}
return f;
}
#if CXX_STD_THREAD
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 */
} /* namespace gdb */
|
