summaryrefslogtreecommitdiff
path: root/Userland/Libraries/LibC/pthread_integration.cpp
blob: f802cd52474001cdba0fd27408831fedd4df8b4c (plain)
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
197
198
199
200
201
202
203
204
205
206
207
208
/*
 * Copyright (c) 2021, the SerenityOS developers.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Atomic.h>
#include <AK/NeverDestroyed.h>
#include <AK/Types.h>
#include <AK/Vector.h>
#include <bits/pthread_integration.h>
#include <errno.h>
#include <sched.h>
#include <serenity.h>
#include <unistd.h>

namespace {

// Most programs don't need this, no need to incur an extra mutex lock/unlock on them
static Atomic<bool> g_did_touch_atfork { false };
static pthread_mutex_t g_atfork_list_mutex __PTHREAD_MUTEX_INITIALIZER;
static NeverDestroyed<Vector<void (*)(void), 4>> g_atfork_prepare_list;
static NeverDestroyed<Vector<void (*)(void), 4>> g_atfork_child_list;
static NeverDestroyed<Vector<void (*)(void), 4>> g_atfork_parent_list;

}

extern "C" {
void __pthread_fork_prepare(void)
{
    if (!g_did_touch_atfork.load())
        return;

    __pthread_mutex_lock(&g_atfork_list_mutex);
    for (auto entry : g_atfork_prepare_list.get())
        entry();
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

void __pthread_fork_child(void)
{
    if (!g_did_touch_atfork.load())
        return;

    __pthread_mutex_lock(&g_atfork_list_mutex);
    for (auto entry : g_atfork_child_list.get())
        entry();
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

void __pthread_fork_parent(void)
{
    if (!g_did_touch_atfork.load())
        return;

    __pthread_mutex_lock(&g_atfork_list_mutex);
    for (auto entry : g_atfork_parent_list.get())
        entry();
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

void __pthread_fork_atfork_register_prepare(void (*func)(void))
{
    g_did_touch_atfork.store(true);

    __pthread_mutex_lock(&g_atfork_list_mutex);
    g_atfork_prepare_list->append(func);
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

void __pthread_fork_atfork_register_parent(void (*func)(void))
{
    g_did_touch_atfork.store(true);

    __pthread_mutex_lock(&g_atfork_list_mutex);
    g_atfork_parent_list->append(func);
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

void __pthread_fork_atfork_register_child(void (*func)(void))
{
    g_did_touch_atfork.store(true);

    __pthread_mutex_lock(&g_atfork_list_mutex);
    g_atfork_child_list->append(func);
    __pthread_mutex_unlock(&g_atfork_list_mutex);
}

int __pthread_self()
{
    return gettid();
}

int pthread_self() __attribute__((weak, alias("__pthread_self")));

static constexpr u32 MUTEX_UNLOCKED = 0;
static constexpr u32 MUTEX_LOCKED_NO_NEED_TO_WAKE = 1;
static constexpr u32 MUTEX_LOCKED_NEED_TO_WAKE = 2;

int __pthread_mutex_init(pthread_mutex_t* mutex, pthread_mutexattr_t const* attributes)
{
    mutex->lock = 0;
    mutex->owner = 0;
    mutex->level = 0;
    mutex->type = attributes ? attributes->type : __PTHREAD_MUTEX_NORMAL;
    return 0;
}

int pthread_mutex_init(pthread_mutex_t*, pthread_mutexattr_t const*) __attribute__((weak, alias("__pthread_mutex_init")));

int __pthread_mutex_trylock(pthread_mutex_t* mutex)
{
    u32 expected = MUTEX_UNLOCKED;
    bool exchanged = AK::atomic_compare_exchange_strong(&mutex->lock, expected, MUTEX_LOCKED_NO_NEED_TO_WAKE, AK::memory_order_acquire);

    if (exchanged) [[likely]] {
        if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
            AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
        mutex->level = 0;
        return 0;
    } else if (mutex->type == __PTHREAD_MUTEX_RECURSIVE) {
        pthread_t owner = AK::atomic_load(&mutex->owner, AK::memory_order_relaxed);
        if (owner == __pthread_self()) {
            // We already own the mutex!
            mutex->level++;
            return 0;
        }
    }
    return EBUSY;
}

int pthread_mutex_trylock(pthread_mutex_t* mutex) __attribute__((weak, alias("__pthread_mutex_trylock")));

int __pthread_mutex_lock(pthread_mutex_t* mutex)
{
    // Fast path: attempt to claim the mutex without waiting.
    u32 value = MUTEX_UNLOCKED;
    bool exchanged = AK::atomic_compare_exchange_strong(&mutex->lock, value, MUTEX_LOCKED_NO_NEED_TO_WAKE, AK::memory_order_acquire);
    if (exchanged) [[likely]] {
        if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
            AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
        mutex->level = 0;
        return 0;
    } else if (mutex->type == __PTHREAD_MUTEX_RECURSIVE) {
        pthread_t owner = AK::atomic_load(&mutex->owner, AK::memory_order_relaxed);
        if (owner == __pthread_self()) {
            // We already own the mutex!
            mutex->level++;
            return 0;
        }
    }

    // Slow path: wait, record the fact that we're going to wait, and always
    // remember to wake the next thread up once we release the mutex.
    if (value != MUTEX_LOCKED_NEED_TO_WAKE)
        value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);

    while (value != MUTEX_UNLOCKED) {
        futex_wait(&mutex->lock, value, nullptr, 0);
        value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);
    }

    if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
        AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
    mutex->level = 0;
    return 0;
}

int pthread_mutex_lock(pthread_mutex_t*) __attribute__((weak, alias("__pthread_mutex_lock")));

int __pthread_mutex_lock_pessimistic_np(pthread_mutex_t* mutex)
{
    // Same as pthread_mutex_lock(), but always set MUTEX_LOCKED_NEED_TO_WAKE,
    // and also don't bother checking for already owning the mutex recursively,
    // because we know we don't. Used in the condition variable implementation.
    u32 value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);
    while (value != MUTEX_UNLOCKED) {
        futex_wait(&mutex->lock, value, nullptr, 0);
        value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);
    }

    if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
        AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
    mutex->level = 0;
    return 0;
}

int __pthread_mutex_unlock(pthread_mutex_t* mutex)
{
    if (mutex->type == __PTHREAD_MUTEX_RECURSIVE && mutex->level > 0) {
        mutex->level--;
        return 0;
    }

    if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
        AK::atomic_store(&mutex->owner, 0, AK::memory_order_relaxed);

    u32 value = AK::atomic_exchange(&mutex->lock, MUTEX_UNLOCKED, AK::memory_order_release);
    if (value == MUTEX_LOCKED_NEED_TO_WAKE) [[unlikely]] {
        int rc = futex_wake(&mutex->lock, 1);
        VERIFY(rc >= 0);
    }

    return 0;
}

int pthread_mutex_unlock(pthread_mutex_t*) __attribute__((weak, alias("__pthread_mutex_unlock")));
}