Revert "[libc] implement cached process/thread identity" (#99559)

Reverts llvm/llvm-project#98989

17 files changed, 29 insertions, 261 deletions

diff --git a/libc/src/__support/OSUtil/CMakeLists.txt b/libc/src/__support/OSUtil/CMakeLists.txt
index 517f888..94d1042 100644
--- a/libc/src/__support/OSUtil/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/CMakeLists.txt
@@ -15,20 +15,3 @@ add_object_library(
   DEPENDS
     ${target_os_util}
 )
-
-if (LIBC_CONF_ENABLE_PID_CACHE)
-  set(libc_copt_enable_pid_cache 1)
-else()
-  set(libc_copt_enable_pid_cache 0)
-endif()
-
-if(TARGET libc.src.__support.OSUtil.${LIBC_TARGET_OS}.pid)
-  add_object_library(
-    pid
-    ALIAS
-    DEPENDS
-      .${LIBC_TARGET_OS}.pid
-    COMPILE_OPTIONS
-      -DLIBC_COPT_ENABLE_PID_CACHE=${libc_copt_enable_pid_cache}
-  )
-endif()
diff --git a/libc/src/__support/OSUtil/linux/CMakeLists.txt b/libc/src/__support/OSUtil/linux/CMakeLists.txt
index 95a83d7..089cad4 100644
--- a/libc/src/__support/OSUtil/linux/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/CMakeLists.txt
@@ -23,16 +23,3 @@ add_object_library(
     libc.hdr.types.struct_f_owner_ex
     libc.hdr.types.off_t
 )
-
-add_object_library(
-  pid
-  SRCS
-    pid.cpp
-  HDRS
-    ../pid.h
-  DEPENDS
-    libc.src.__support.OSUtil.osutil
-    libc.src.__support.common
-    libc.hdr.types.pid_t
-    libc.include.sys_syscall
-)
diff --git a/libc/src/__support/OSUtil/linux/pid.cpp b/libc/src/__support/OSUtil/linux/pid.cpp
deleted file mode 100644
index a8499af..0000000
--- a/libc/src/__support/OSUtil/linux/pid.cpp
+++ /dev/null
@@ -1,20 +0,0 @@
-//===------------ pid_t utilities implementation ----------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "src/__support/OSUtil/pid.h"
-#include "src/__support/OSUtil/syscall.h"
-#include <sys/syscall.h>
-
-namespace LIBC_NAMESPACE_DECL {
-
-pid_t ProcessIdentity::cache = -1;
-pid_t ProcessIdentity::get_uncached() {
-  return syscall_impl<pid_t>(SYS_getpid);
-}
-
-} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/OSUtil/pid.h b/libc/src/__support/OSUtil/pid.h
deleted file mode 100644
index d723abe..0000000
--- a/libc/src/__support/OSUtil/pid.h
+++ /dev/null
@@ -1,41 +0,0 @@
-//===------------ pid_t utilities -------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
-#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
-#include "hdr/types/pid_t.h"
-#include "src/__support/macros/attributes.h"
-#include "src/__support/macros/optimization.h"
-
-#ifndef LIBC_COPT_ENABLE_PID_CACHE
-#define LIBC_COPT_ENABLE_PID_CACHE 1
-#endif
-
-namespace LIBC_NAMESPACE_DECL {
-
-class ProcessIdentity {
-  static LIBC_INLINE_VAR thread_local bool fork_inflight = true;
-  static pid_t cache;
-  static pid_t get_uncached();
-
-public:
-  LIBC_INLINE static void start_fork() { fork_inflight = true; }
-  LIBC_INLINE static void end_fork() { fork_inflight = false; }
-  LIBC_INLINE static void refresh_cache() { cache = get_uncached(); }
-  LIBC_INLINE static pid_t get() {
-#if LIBC_COPT_ENABLE_PID_CACHE
-    if (LIBC_LIKELY(!fork_inflight))
-      return cache;
-#endif
-    return get_uncached();
-  }
-};
-
-} // namespace LIBC_NAMESPACE_DECL
-
-#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
diff --git a/libc/src/__support/threads/CMakeLists.txt b/libc/src/__support/threads/CMakeLists.txt
index f1a2f16..d2e46b8 100644
--- a/libc/src/__support/threads/CMakeLists.txt
+++ b/libc/src/__support/threads/CMakeLists.txt
@@ -44,12 +44,6 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.mutex)
   )
 endif()
 
-if (LIBC_CONF_ENABLE_TID_CACHE)
-  set(libc_copt_enable_tid_cache 1)
-else()
-  set(libc_copt_enable_tid_cache 0)
-endif()
-
 add_header_library(
   thread_common
   HDRS
@@ -60,9 +54,6 @@ add_header_library(
     libc.src.__support.CPP.optional
     libc.src.__support.CPP.string_view
     libc.src.__support.CPP.stringstream
-    libc.hdr.types.pid_t
-  COMPILE_OPTIONS
-    -DLIBC_COPT_ENABLE_TID_CACHE=${libc_copt_enable_tid_cache}
 )
 
 if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.thread)
@@ -98,21 +89,3 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.CndVar)
     .${LIBC_TARGET_OS}.CndVar
   )
 endif()
-
-set(tid_dep)
-if (LLVM_LIBC_FULL_BUILD)
-  list(APPEND tid_dep libc.src.__support.thread)
-else()
-  list(APPEND tid_dep libc.src.__support.OSUtil.osutil)
-  list(APPEND tid_dep libc.include.sys_syscall)
-endif()
-
-add_header_library(
-  tid
-  HDRS
-    tid.h
-  DEPENDS
-    libc.src.__support.common
-    libc.hdr.types.pid_t
-    ${tid_dep}
-)
diff --git a/libc/src/__support/threads/linux/CMakeLists.txt b/libc/src/__support/threads/linux/CMakeLists.txt
index d86441d..8b79715 100644
--- a/libc/src/__support/threads/linux/CMakeLists.txt
+++ b/libc/src/__support/threads/linux/CMakeLists.txt
@@ -55,7 +55,6 @@ add_header_library(
     libc.src.__support.common
     libc.src.__support.OSUtil.osutil
     libc.src.__support.CPP.limits
-    libc.src.__support.threads.tid
   COMPILE_OPTIONS
     -DLIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT=${LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT}
     ${monotonicity_flags}
diff --git a/libc/src/__support/threads/linux/rwlock.h b/libc/src/__support/threads/linux/rwlock.h
index cae8aa6..d2fb0ce 100644
--- a/libc/src/__support/threads/linux/rwlock.h
+++ b/libc/src/__support/threads/linux/rwlock.h
@@ -23,7 +23,6 @@
 #include "src/__support/threads/linux/futex_word.h"
 #include "src/__support/threads/linux/raw_mutex.h"
 #include "src/__support/threads/sleep.h"
-#include "src/__support/threads/tid.h"
 
 #ifndef LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT
 #define LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT 100
@@ -337,6 +336,8 @@ private:
   LIBC_INLINE Role get_preference() const {
     return static_cast<Role>(preference);
   }
+  // TODO: use cached thread id once implemented.
+  LIBC_INLINE static pid_t gettid() { return syscall_impl<pid_t>(SYS_gettid); }
 
   template <Role role> LIBC_INLINE LockResult try_lock(RwState &old) {
     if constexpr (role == Role::Reader) {
@@ -358,7 +359,7 @@ private:
         if (LIBC_LIKELY(old.compare_exchange_weak_with(
                 state, old.set_writer_bit(), cpp::MemoryOrder::ACQUIRE,
                 cpp::MemoryOrder::RELAXED))) {
-          writer_tid.store(gettid_inline(), cpp::MemoryOrder::RELAXED);
+          writer_tid.store(gettid(), cpp::MemoryOrder::RELAXED);
           return LockResult::Success;
         }
         // Notice that old is updated by the compare_exchange_weak_with
@@ -393,7 +394,7 @@ private:
             unsigned spin_count = LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT) {
     // Phase 1: deadlock detection.
     // A deadlock happens if this is a RAW/WAW lock in the same thread.
-    if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid_inline())
+    if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid())
       return LockResult::Deadlock;
 
 #if LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
@@ -519,7 +520,7 @@ public:
     if (old.has_active_writer()) {
       // The lock is held by a writer.
       // Check if we are the owner of the lock.
-      if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid_inline())
+      if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid())
         return LockResult::PermissionDenied;
       // clear writer tid.
       writer_tid.store(0, cpp::MemoryOrder::RELAXED);
diff --git a/libc/src/__support/threads/linux/thread.cpp b/libc/src/__support/threads/linux/thread.cpp
index c8ad086..36b4a88 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -518,6 +518,4 @@ void thread_exit(ThreadReturnValue retval, ThreadStyle style) {
   __builtin_unreachable();
 }
 
-pid_t Thread::get_uncached_tid() { return syscall_impl<pid_t>(SYS_gettid); }
-
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/threads/thread.h b/libc/src/__support/threads/thread.h
index 1805b6f..ce23a88 100644
--- a/libc/src/__support/threads/thread.h
+++ b/libc/src/__support/threads/thread.h
@@ -9,11 +9,6 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
 #define LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
 
-#ifndef LIBC_COPT_ENABLE_TID_CACHE
-#define LIBC_COPT_ENABLE_TID_CACHE 1
-#endif
-
-#include "hdr/types/pid_t.h"
 #include "src/__support/CPP/atomic.h"
 #include "src/__support/CPP/optional.h"
 #include "src/__support/CPP/string_view.h"
@@ -108,7 +103,7 @@ struct alignas(STACK_ALIGNMENT) ThreadAttributes {
   uintptr_t tls;                // Address to the thread TLS memory
   uintptr_t tls_size;           // The size of area pointed to by |tls|.
   unsigned char owned_stack; // Indicates if the thread owns this stack memory
-  pid_t tid;
+  int tid;
   ThreadStyle style;
   ThreadReturnValue retval;
   ThreadAtExitCallbackMgr *atexit_callback_mgr;
@@ -233,26 +228,6 @@ struct Thread {
 
   // Return the name of the thread in |name|. Return the error number of error.
   int get_name(cpp::StringStream &name) const;
-
-  static pid_t get_uncached_tid();
-
-  LIBC_INLINE void refresh_tid(pid_t cached = -1) {
-    if (cached >= 0)
-      this->attrib->tid = cached;
-    else
-      this->attrib->tid = get_uncached_tid();
-  }
-  LIBC_INLINE void invalidate_tid() { this->attrib->tid = -1; }
-
-  LIBC_INLINE pid_t get_tid() {
-#if LIBC_COPT_ENABLE_TID_CACHE
-    if (LIBC_UNLIKELY(this->attrib->tid < 0))
-      return get_uncached_tid();
-    return this->attrib->tid;
-#else
-    return get_uncached_tid();
-#endif
-  }
 };
 
 extern LIBC_THREAD_LOCAL Thread self;
diff --git a/libc/src/__support/threads/tid.h b/libc/src/__support/threads/tid.h
deleted file mode 100644
index a575cff..0000000
--- a/libc/src/__support/threads/tid.h
+++ /dev/null
@@ -1,34 +0,0 @@
-//===--- Tid wrapper --------------------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
-#define LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
-
-// This header is for internal usage which automatically dispatches full build
-// and overlay build behaviors.
-
-#include "hdr/types/pid_t.h"
-#include "src/__support/common.h"
-#ifdef LIBC_FULL_BUILD
-#include "src/__support/threads/thread.h"
-#else
-#include "src/__support/OSUtil/syscall.h"
-#include <sys/syscall.h>
-#endif // LIBC_FULL_BUILD
-
-namespace LIBC_NAMESPACE_DECL {
-LIBC_INLINE pid_t gettid_inline() {
-#ifdef LIBC_FULL_BUILD
-  return self.get_tid();
-#else
-  return syscall_impl<pid_t>(SYS_gettid);
-#endif
-}
-} // namespace LIBC_NAMESPACE_DECL
-
-#endif // LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index ec76712..ddafcd7 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -333,13 +333,3 @@ add_entrypoint_external(
 add_entrypoint_external(
   opterr
 )
-
-add_entrypoint_object(
-  gettid
-  SRCS
-    gettid.cpp
-  HDRS
-    gettid.h
-  DEPENDS
-    libc.src.__support.threads.tid
-)
diff --git a/libc/src/unistd/getpid.h b/libc/src/unistd/getpid.h
index 5812df0..c3c55b0 100644
--- a/libc/src/unistd/getpid.h
+++ b/libc/src/unistd/getpid.h
@@ -9,12 +9,12 @@
 #ifndef LLVM_LIBC_SRC_UNISTD_GETPID_H
 #define LLVM_LIBC_SRC_UNISTD_GETPID_H
 
-#include "hdr/types/pid_t.h"
 #include "src/__support/macros/config.h"
+#include <unistd.h>
 
 namespace LIBC_NAMESPACE_DECL {
 
-pid_t getpid(void);
+pid_t getpid();
 
 } // namespace LIBC_NAMESPACE_DECL
 
diff --git a/libc/src/unistd/gettid.cpp b/libc/src/unistd/gettid.cpp
deleted file mode 100644
index 6d8ed65..0000000
--- a/libc/src/unistd/gettid.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-//===-- Implementation file for gettid --------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "src/unistd/gettid.h"
-#include "src/__support/common.h"
-#include "src/__support/threads/tid.h"
-
-namespace LIBC_NAMESPACE_DECL {
-
-LLVM_LIBC_FUNCTION(pid_t, gettid, (void)) { return gettid_inline(); }
-
-} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/unistd/gettid.h b/libc/src/unistd/gettid.h
deleted file mode 100644
index 4228319..0000000
--- a/libc/src/unistd/gettid.h
+++ /dev/null
@@ -1,21 +0,0 @@
-//===-- Implementation header for gettid ------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_LIBC_SRC_UNISTD_GETTID_H
-#define LLVM_LIBC_SRC_UNISTD_GETTID_H
-
-#include "hdr/types/pid_t.h"
-#include "src/__support/common.h"
-
-namespace LIBC_NAMESPACE_DECL {
-
-pid_t gettid(void);
-
-} // namespace LIBC_NAMESPACE_DECL
-
-#endif // LLVM_LIBC_SRC_UNISTD_GETTID_H
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
index 651ea60..7e733d7 100644
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -101,7 +101,6 @@ add_entrypoint_object(
     libc.include.sys_syscall
     libc.src.__support.threads.fork_callbacks
     libc.src.__support.OSUtil.osutil
-    libc.src.__support.OSUtil.pid
     libc.src.__support.threads.thread
     libc.src.errno.errno
 )
@@ -205,7 +204,8 @@ add_entrypoint_object(
     ../getpid.h
   DEPENDS
     libc.include.unistd
-    libc.src.__support.OSUtil.pid
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
 )
 
 add_entrypoint_object(
diff --git a/libc/src/unistd/linux/fork.cpp b/libc/src/unistd/linux/fork.cpp
index 8fe1881..7d47665 100644
--- a/libc/src/unistd/linux/fork.cpp
+++ b/libc/src/unistd/linux/fork.cpp
@@ -8,14 +8,13 @@
 
 #include "src/unistd/fork.h"
 
-#include "src/__support/OSUtil/pid.h"
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
 #include "src/__support/threads/fork_callbacks.h"
 #include "src/__support/threads/thread.h" // For thread self object
-#include "src/errno/libc_errno.h"
 
+#include "src/errno/libc_errno.h"
 #include <signal.h>      // For SIGCHLD
 #include <sys/syscall.h> // For syscall numbers.
 
@@ -26,14 +25,6 @@ namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
   invoke_prepare_callbacks();
-
-  // Invalidate tid/pid cache before fork to avoid post fork signal handler from
-  // getting wrong values. gettid() is not async-signal-safe, but let's provide
-  // our best efforts here.
-  pid_t parent_tid = self.get_tid();
-  self.invalidate_tid();
-  ProcessIdentity::start_fork();
-
 #ifdef SYS_fork
   pid_t ret = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_fork);
 #elif defined(SYS_clone)
@@ -41,6 +32,15 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
 #else
 #error "fork and clone syscalls not available."
 #endif
+  if (ret == 0) {
+    // Return value is 0 in the child process.
+    // The child is created with a single thread whose self object will be a
+    // copy of parent process' thread which called fork. So, we have to fix up
+    // the child process' self object with the new process' tid.
+    self.attrib->tid = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_gettid);
+    invoke_child_callbacks();
+    return 0;
+  }
 
   if (ret < 0) {
     // Error case, a child process was not created.
@@ -48,18 +48,6 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
     return -1;
   }
 
-  // Child process
-  if (ret == 0) {
-    self.refresh_tid();
-    ProcessIdentity::refresh_cache();
-    ProcessIdentity::end_fork();
-    invoke_child_callbacks();
-    return 0;
-  }
-
-  // Parent process
-  self.refresh_tid(parent_tid);
-  ProcessIdentity::end_fork();
   invoke_parent_callbacks();
   return ret;
 }
diff --git a/libc/src/unistd/linux/getpid.cpp b/libc/src/unistd/linux/getpid.cpp
index 65d6c8a..b24c86a 100644
--- a/libc/src/unistd/linux/getpid.cpp
+++ b/libc/src/unistd/linux/getpid.cpp
@@ -7,10 +7,17 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/unistd/getpid.h"
-#include "src/__support/OSUtil/pid.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
 namespace LIBC_NAMESPACE_DECL {
 
-LLVM_LIBC_FUNCTION(pid_t, getpid, (void)) { return ProcessIdentity::get(); }
+LLVM_LIBC_FUNCTION(pid_t, getpid, ()) {
+  return LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_getpid);
+}
 
 } // namespace LIBC_NAMESPACE_DECL