From 0b8ac37450c0564abcff0a789afca7dee9aedca7 Mon Sep 17 00:00:00 2001
From: Leonid Yuriev <leo@yuriev.ru>
Date: Tue, 16 Jul 2019 11:52:10 +0300
Subject: [PATCH] mdbx: reduces number of getpid() calls for checking PID
 against fork().

PID check could be ommited:
 - on Linux when madvise(MADV_DONTFORK) is available. i.e. after the fork()
    mapped pages will not be available for child process.
 - in Windows where fork() not available.

Change-Id: I4dd6bcb209cfc816ae3ec43825ea913d2249663c
---
 src/bits.h | 13 +++++++++++++
 src/mdbx.c | 12 ++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/bits.h b/src/bits.h
index 610f15eb..52e89f45 100644
--- a/src/bits.h
+++ b/src/bits.h
@@ -1213,3 +1213,16 @@ static __inline void mdbx_jitter4testing(bool tiny) {
   (void)tiny;
 #endif
 }
+
+/* Controls checking PID against reuse DB environment after the fork() */
+#ifndef MDBX_TXN_CHECKPID
+#if defined(MADV_DONTFORK) || defined(_WIN32) || defined(_WIN64)
+/* PID check could be ommited:
+ *  - on Linux when madvise(MADV_DONTFORK) is available. i.e. after the fork()
+ *    mapped pages will not be available for child process.
+ *  - in Windows where fork() not available. */
+#define MDBX_TXN_CHECKPID 0
+#else
+#define MDBX_TXN_CHECKPID 1
+#endif
+#endif /* MDBX_TXN_CHECKPID */
diff --git a/src/mdbx.c b/src/mdbx.c
index c70539c1..3bae1077 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -3155,10 +3155,12 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
   MDBX_env *env = txn->mt_env;
   int rc;
 
+#if MDBX_TXN_CHECKPID
   if (unlikely(env->me_pid != mdbx_getpid())) {
     env->me_flags |= MDBX_FATAL_ERROR;
     return MDBX_PANIC;
   }
+#endif /* MDBX_TXN_CHECKPID */
 
   STATIC_ASSERT(sizeof(MDBX_reader) == MDBX_CACHELINE_SIZE);
   STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_numreaders) % MDBX_CACHELINE_SIZE ==
@@ -3436,8 +3438,10 @@ int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, unsigned flags,
   if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
     return MDBX_EBADSIGN;
 
+#if MDBX_TXN_CHECKPID
   if (unlikely(env->me_pid != mdbx_getpid()))
     env->me_flags |= MDBX_FATAL_ERROR;
+#endif /* MDBX_TXN_CHECKPID */
 
   if (unlikely(env->me_flags & MDBX_FATAL_ERROR))
     return MDBX_PANIC;
@@ -3635,10 +3639,12 @@ static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
   MDBX_env *env = txn->mt_env;
   static const char *const names[] = MDBX_END_NAMES;
 
+#if MDBX_TXN_CHECKPID
   if (unlikely(txn->mt_env->me_pid != mdbx_getpid())) {
     env->me_flags |= MDBX_FATAL_ERROR;
     return MDBX_PANIC;
   }
+#endif /* MDBX_TXN_CHECKPID */
 
   mdbx_debug("%s txn %" PRIaTXN "%c %p on mdbenv %p, root page %" PRIaPGNO
              "/%" PRIaPGNO,
@@ -4719,10 +4725,12 @@ int mdbx_txn_commit(MDBX_txn *txn) {
     return MDBX_THREAD_MISMATCH;
 
   MDBX_env *env = txn->mt_env;
+#if MDBX_TXN_CHECKPID
   if (unlikely(env->me_pid != mdbx_getpid())) {
     env->me_flags |= MDBX_FATAL_ERROR;
     return MDBX_PANIC;
   }
+#endif /* MDBX_TXN_CHECKPID */
 
   if (txn->mt_child) {
     rc = mdbx_txn_commit(txn->mt_child);
@@ -5716,8 +5724,10 @@ mdbx_env_set_geometry(MDBX_env *env, intptr_t size_lower, intptr_t size_now,
   if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
     return MDBX_EBADSIGN;
 
+#if MDBX_TXN_CHECKPID
   if (unlikely(env->me_pid != mdbx_getpid()))
     env->me_flags |= MDBX_FATAL_ERROR;
+#endif /* MDBX_TXN_CHECKPID */
 
   if (unlikely(env->me_flags & MDBX_FATAL_ERROR))
     return MDBX_PANIC;
@@ -12636,10 +12646,12 @@ int __cold mdbx_reader_check(MDBX_env *env, int *dead) {
 int __cold mdbx_reader_check0(MDBX_env *env, int rdt_locked, int *dead) {
   mdbx_assert(env, rdt_locked >= 0);
 
+#if MDBX_TXN_CHECKPID
   if (unlikely(env->me_pid != mdbx_getpid())) {
     env->me_flags |= MDBX_FATAL_ERROR;
     return MDBX_PANIC;
   }
+#endif /* MDBX_TXN_CHECKPID */
 
   MDBX_lockinfo *const lck = env->me_lck;
   if (unlikely(lck == NULL)) {