From 35b3fbd90c2ad2c503c9e3d28bfbffff13099925 Mon Sep 17 00:00:00 2001
From: Binbin <binloveplay1314@qq.com>
Date: Sun, 9 Oct 2022 13:18:34 +0800
Subject: Freeze time sampling during command execution, and scripts (#10300)

Freeze time during execution of scripts and all other commands.
This means that a key is either expired or not, and doesn't change
state during a script execution. resolves #10182

This PR try to add a new `commandTimeSnapshot` function.
The function logic is extracted from `keyIsExpired`, but the related
calls to `fixed_time_expire` and `mstime()` are removed, see below.

In commands, we will avoid calling `mstime()` multiple times
and just use the one that sampled in call. The background is,
e.g. using `PEXPIRE 1` with valgrind sometimes result in the key
being deleted rather than expired. The reason is that both `PEXPIRE`
command and `checkAlreadyExpired` call `mstime()` separately.

There are other more important changes in this PR:
1. Eliminate `fixed_time_expire`, it is no longer needed.
   When we want to sample time we should always use a time snapshot.
   We will use `in_nested_call` instead to update the cached time in `call`.
2. Move the call for `updateCachedTime` from `serverCron` to `afterSleep`.
    Now `commandTimeSnapshot` will always return the sample time, the
    `lookupKeyReadWithFlags` call in `getNodeByQuery` will get a outdated
    cached time (because `processCommand` is out of the `call` context).
    We put the call to `updateCachedTime` in `aftersleep`.
3. Cache the time each time the module lock Redis.
    Call `updateCachedTime` in `moduleGILAfterLock`, affecting `RM_ThreadSafeContextLock`
    and `RM_ThreadSafeContextTryLock`

Currently the commandTimeSnapshot change affects the following TTL commands:
- SET EX / SET PX
- EXPIRE / PEXPIRE
- SETEX / PSETEX
- GETEX EX / GETEX PX
- TTL / PTTL
- EXPIRETIME / PEXPIRETIME
- RESTORE key TTL

And other commands just use the cached mstime (including TIME).

This is considered to be a breaking change since it can break a script
that uses a loop to wait for a key to expire.
---
 src/server.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'src/server.h')

diff --git a/src/server.h b/src/server.h
index 74e4098db..2ec7dc7ea 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1520,7 +1520,6 @@ struct redisServer {
     clientMemUsageBucket client_mem_usage_buckets[CLIENT_MEM_USAGE_BUCKETS];
 
     rax *clients_timeout_table; /* Radix tree for blocked clients timeouts. */
-    long fixed_time_expire;     /* If > 0, expire keys against server.mstime. */
     int in_nested_call;         /* If > 0, in a nested call of a call */
     rax *clients_index;         /* Active clients dictionary by client ID. */
     pause_type client_pause_type;      /* True if clients are currently paused */
@@ -2420,7 +2419,8 @@ int moduleIsModuleCommand(void *module_handle, struct redisCommand *cmd);
 
 /* Utils */
 long long ustime(void);
-long long mstime(void);
+mstime_t mstime(void);
+mstime_t commandTimeSnapshot(void);
 void getRandomHexChars(char *p, size_t len);
 void getRandomBytes(unsigned char *p, size_t len);
 uint64_t crc64(uint64_t crc, const unsigned char *s, uint64_t l);
-- 
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