rpc/blockchain.cpp: Remove g_utxosetscan mutex that is only protecting a single atomic variable

ajtowns · ajtowns · commit c3cf2f55013c · 2020-05-06T15:28:49.000+10:00
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
@@ -1976,7 +1976,6 @@ bool FindScriptPubKey(std::atomic<int>& scan_progress, const std::atomic<bool>&
 }
 
 /** RAII object to prevent concurrency issue when scanning the txout set */
-static std::mutex g_utxosetscan;
 static std::atomic<int> g_scan_progress;
 static std::atomic<bool> g_scan_in_progress;
 static std::atomic<bool> g_should_abort_scan;
@@ -1989,18 +1988,15 @@ class CoinsViewScanReserver
 
     bool reserve() {
         CHECK_NONFATAL(!m_could_reserve);
-        std::lock_guard<std::mutex> lock(g_utxosetscan);
-        if (g_scan_in_progress) {
+        if (g_scan_in_progress.exchange(true)) {
             return false;
         }
-        g_scan_in_progress = true;
         m_could_reserve = true;
         return true;
     }
 
     ~CoinsViewScanReserver() {
         if (m_could_reserve) {
-            std::lock_guard<std::mutex> lock(g_utxosetscan);
             g_scan_in_progress = false;
         }
     }

Original file line number	Diff line number	Diff line change
`@@ -1976,7 +1976,6 @@ bool FindScriptPubKey(std::atomic<int>& scan_progress, const std::atomic<bool>&`
`1976`	`1976`	`}`
`1977`	`1977`
`1978`	`1978`	`/** RAII object to prevent concurrency issue when scanning the txout set */`
`1979`		`-static std::mutex g_utxosetscan;`
`1980`	`1979`	`static std::atomic<int> g_scan_progress;`
`1981`	`1980`	`static std::atomic<bool> g_scan_in_progress;`
`1982`	`1981`	`static std::atomic<bool> g_should_abort_scan;`
`@@ -1989,18 +1988,15 @@ class CoinsViewScanReserver`
`1989`	`1988`
`1990`	`1989`	`bool reserve() {`
`1991`	`1990`	`CHECK_NONFATAL(!m_could_reserve);`
`1992`		`- std::lock_guard<std::mutex> lock(g_utxosetscan);`
`1993`		`- if (g_scan_in_progress) {`
	`1991`	`+ if (g_scan_in_progress.exchange(true)) {`
`1994`	`1992`	`return false;`
`1995`	`1993`	`}`
`1996`		`- g_scan_in_progress = true;`
`1997`	`1994`	`m_could_reserve = true;`
`1998`	`1995`	`return true;`
`1999`	`1996`	`}`
`2000`	`1997`
`2001`	`1998`	`~CoinsViewScanReserver() {`
`2002`	`1999`	`if (m_could_reserve) {`
`2003`		`- std::lock_guard<std::mutex> lock(g_utxosetscan);`
`2004`	`2000`	`g_scan_in_progress = false;`
`2005`	`2001`	`}`
`2006`	`2002`	`}`