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LibC+LibPthread: Implement function forwarding for libpthread

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GCC will insert various calls to pthread functions when compiling
C++ code with static initializers, even when the user doesn't link
their program against libpthread explicitly.

This is used to make static initializers thread-safe, e.g. when
building a library that does not itself use thread functionality
and thus does not link against libpthread - but is intended to
be used with other code that does use libpthread explicitly.

This makes these symbols available in libc.
This commit is contained in:
Gunnar Beutner 2021-04-17 18:38:32 +02:00 • committed by Andreas Kling
parent db3fd11646
commit 88cebb05ad
14 changed files with 381 additions and 100 deletions
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90
Userland/Libraries/LibPthread/pthread.cpp
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@ -55,8 +55,6 @@ constexpr size_t highest_reasonable_stack_size = 8 * MiB; // That's the default
#define __RETURN_PTHREAD_ERROR(rc) \
return ((rc) < 0 ? -(rc) : 0)
extern void (*__libc_pthread_key_destroy_for_current_thread)();
extern "C" {
static void* pthread_create_helper(void* (*routine)(void*), void* argument)
@ -531,99 +529,31 @@ int pthread_cond_broadcast(pthread_cond_t* cond)
return 0;
}
static constexpr int max_keys = PTHREAD_KEYS_MAX;
typedef void (*KeyDestructor)(void*);
struct KeyTable {
KeyDestructor destructors[max_keys] { nullptr };
int next { 0 };
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
};
struct SpecificTable {
void* values[max_keys] { nullptr };
};
static KeyTable s_keys;
__thread SpecificTable t_specifics;
// libgcc expects this function to exist in libpthread, even
// if it is not implemented.
int pthread_cancel(pthread_t)
{
TODO();
}
int pthread_key_create(pthread_key_t* key, KeyDestructor destructor)
{
int ret = 0;
pthread_mutex_lock(&s_keys.mutex);
if (s_keys.next >= max_keys) {
ret = EAGAIN;
} else {
*key = s_keys.next++;
s_keys.destructors[*key] = destructor;
ret = 0;
}
pthread_mutex_unlock(&s_keys.mutex);
return ret;
return __pthread_key_create(key, destructor);
}
int pthread_key_delete(pthread_key_t key)
{
if (key < 0 || key >= max_keys)
return EINVAL;
pthread_mutex_lock(&s_keys.mutex);
s_keys.destructors[key] = nullptr;
pthread_mutex_unlock(&s_keys.mutex);
return 0;
return __pthread_key_delete(key);
}
void* pthread_getspecific(pthread_key_t key)
{
if (key < 0)
return nullptr;
if (key >= max_keys)
return nullptr;
return t_specifics.values[key];
return __pthread_getspecific(key);
}
int pthread_setspecific(pthread_key_t key, const void* value)
{
if (key < 0)
return EINVAL;
if (key >= max_keys)
return EINVAL;
t_specifics.values[key] = const_cast<void*>(value);
return 0;
}
[[gnu::constructor]] static void set_libc_key_destructor()
{
__libc_pthread_key_destroy_for_current_thread = __pthread_key_destroy_for_current_thread;
}
void __pthread_key_destroy_for_current_thread()
{
// This function will either be called during exit_thread, for a pthread, or
// during global program shutdown for the main thread.
pthread_mutex_lock(&s_keys.mutex);
size_t num_used_keys = s_keys.next;
// Dr. POSIX accounts for weird key destructors setting their own key again.
// Or even, setting other unrelated keys? Odd, but whatever the Doc says goes.
for (size_t destruct_iteration = 0; destruct_iteration < PTHREAD_DESTRUCTOR_ITERATIONS; ++destruct_iteration) {
bool any_nonnull_destructors = false;
for (size_t key_index = 0; key_index < num_used_keys; ++key_index) {
void* value = exchange(t_specifics.values[key_index], nullptr);
if (value && s_keys.destructors[key_index]) {
any_nonnull_destructors = true;
(*s_keys.destructors[key_index])(value);
}
}
if (!any_nonnull_destructors)
break;
}
pthread_mutex_unlock(&s_keys.mutex);
return __pthread_setspecific(key, value);
}
int pthread_setname_np(pthread_t thread, const char* name)