Fix segfaults (#561)

* skString c_str contains string encoded in UTF8, but it was treated as UTF16

* ensure that managedString doesn't collect til the end of JNI call, also close manually at the end

skiko/src/commonMain/kotlin/org/jetbrains/skia/shaper/Shaper.kt

@@ -105,8 +105,8 @@ class Shaper internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
     fun shape(text: String, font: Font, opts: ShapingOptions, width: Float, offset: Point): TextBlob? {
         return try {
             Stats.onNativeCall()
-            val managedString = ManagedString(text)
-            val ptr = interopScope {
+            val ptr = ManagedString(text).use { managedString ->
+                interopScope {
                     _nShapeBlob(
                         _ptr,
                         managedString._ptr,
@@ -119,6 +119,7 @@ class Shaper internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
                         offsetY = offset.y
                     )
                 }
+            }
             if (NullPointer == ptr) null else TextBlob(ptr)
         } finally {
             reachabilityBarrier(this)

skiko/src/jvmMain/cpp/common/Font.cc

@@ -227,7 +227,10 @@ extern "C" JNIEXPORT jshort JNICALL Java_org_jetbrains_skia_FontKt__1nGetUTF32Gl
 extern "C" JNIEXPORT jint JNICALL Java_org_jetbrains_skia_FontKt__1nGetStringGlyphsCount
   (JNIEnv* env, jclass jclass, jlong ptr, jstring str, jint len) {
     SkFont* instance = reinterpret_cast<SkFont*>(static_cast<uintptr_t>(ptr));
-    return instance->countText(skString(env, str).c_str(), len * sizeof(jchar), SkTextEncoding::kUTF16);
+    const jchar* chars = env->GetStringCritical(str, nullptr);
+    jint result = instance->countText(chars, len * sizeof(jchar), SkTextEncoding::kUTF16);
+    env->ReleaseStringCritical(str, chars);
+    return result;
 }
 
 extern "C" JNIEXPORT void JNICALL Java_org_jetbrains_skia_FontKt__1nMeasureText
@@ -246,7 +249,10 @@ extern "C" JNIEXPORT jfloat JNICALL Java_org_jetbrains_skia_FontKt__1nMeasureTex
   (JNIEnv* env, jclass jclass, jlong ptr, jstring str, jint len, jlong paintPtr) {
     SkFont* instance = reinterpret_cast<SkFont*>(static_cast<uintptr_t>(ptr));
     SkPaint* paint = reinterpret_cast<SkPaint*>(static_cast<uintptr_t>(paintPtr));
-    return instance->measureText(skString(env, str).c_str(), len * sizeof(jchar), SkTextEncoding::kUTF16, nullptr, paint);
+    const jchar* chars = env->GetStringCritical(str, nullptr);
+    jfloat result = instance->measureText(chars, len * sizeof(jchar), SkTextEncoding::kUTF16, nullptr, paint);
+    env->ReleaseStringCritical(str, chars);
+    return result;
 }
 
 extern "C" JNIEXPORT void JNICALL Java_org_jetbrains_skia_FontKt__1nGetWidths