From 7dfe68cac6e3ed26deb842d70f641264fd604071 Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.a.alekhin@gmail.com>
Date: Sun, 13 Sep 2020 11:14:56 +0000
Subject: [PATCH] imgcodecs: lazy on-demand codecs initialization

---
 modules/imgcodecs/src/loadsave.cpp | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/modules/imgcodecs/src/loadsave.cpp b/modules/imgcodecs/src/loadsave.cpp
index ddd5fcf6fa..4e626cd216 100644
--- a/modules/imgcodecs/src/loadsave.cpp
+++ b/modules/imgcodecs/src/loadsave.cpp
@@ -189,7 +189,19 @@ struct ImageCodecInitializer
     std::vector<ImageEncoder> encoders;
 };
 
-static ImageCodecInitializer codecs;
+static
+ImageCodecInitializer& getCodecs()
+{
+#ifdef CV_CXX11
+    static ImageCodecInitializer g_codecs;
+    return g_codecs;
+#else
+    // C++98 doesn't guarantee correctness of multi-threaded initialization of static global variables
+    // (memory leak here is not critical, use C++11 to avoid that)
+    static ImageCodecInitializer* g_codecs = new ImageCodecInitializer();
+    return *g_codecs;
+#endif
+}
 
 /**
  * Find the decoders
@@ -203,6 +215,7 @@ static ImageDecoder findDecoder( const String& filename ) {
     size_t i, maxlen = 0;
 
     /// iterate through list of registered codecs
+    ImageCodecInitializer& codecs = getCodecs();
     for( i = 0; i < codecs.decoders.size(); i++ )
     {
         size_t len = codecs.decoders[i]->signatureLength();
@@ -240,6 +253,7 @@ static ImageDecoder findDecoder( const Mat& buf )
     if( buf.rows*buf.cols < 1 || !buf.isContinuous() )
         return ImageDecoder();
 
+    ImageCodecInitializer& codecs = getCodecs();
     for( i = 0; i < codecs.decoders.size(); i++ )
     {
         size_t len = codecs.decoders[i]->signatureLength();
@@ -272,6 +286,7 @@ static ImageEncoder findEncoder( const String& _ext )
     for( ext++; len < 128 && isalnum(ext[len]); len++ )
         ;
 
+    ImageCodecInitializer& codecs = getCodecs();
     for( size_t i = 0; i < codecs.encoders.size(); i++ )
     {
         String description = codecs.encoders[i]->getDescription();