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LibC: Cache the result of gettid() to avoid syscalls

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We now use minherit(MAP_INHERIT_ZERO) to create a gettid() cache that
is automatically invalidated on fork(). This is needed since the TID
will be different in a forked child, and so we can't have a stale
cached TID lying around.

This is a gigantic speedup for LibJS (and everyone else too) :^)
This commit is contained in:
Andreas Kling 2020-04-12 20:23:18 +02:00
parent c19b56dc99
commit c84b8e597a
1 changed files with 20 additions and 1 deletions
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21
Libraries/LibC/unistd.cpp
View file

@ -39,6 +39,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <termios.h>
#include <unistd.h>
@ -547,9 +548,27 @@ int ftruncate(int fd, off_t length)
__RETURN_WITH_ERRNO(rc, rc, -1);
}
struct ThreadInfoCache {
int tid { 0 };
};
__thread ThreadInfoCache* thread_info_cache;
int gettid()
{
return syscall(SC_gettid);
if (!thread_info_cache) {
thread_info_cache = (ThreadInfoCache*)mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
ASSERT(thread_info_cache != MAP_FAILED);
if (minherit(thread_info_cache, PAGE_SIZE, MAP_INHERIT_ZERO) < 0) {
perror("minherit(MAP_INHERIT_ZERO)");
ASSERT_NOT_REACHED();
}
}
if (thread_info_cache->tid == 0)
thread_info_cache->tid = syscall(SC_gettid);
return thread_info_cache->tid;
}
int donate(int tid)