Changed usage of mutex with update method of mutable state flow to atomically update values of it.

JetNews/app/src/main/java/com/example/jetnews/data/interests/impl/FakeInterestsRepository.kt

@@ -24,8 +24,7 @@ import com.example.jetnews.utils.addOrRemove
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
-import kotlinx.coroutines.sync.Mutex
-import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.flow.update
 
 /**
  * Implementation of InterestRepository that returns a hardcoded list of
@@ -78,9 +77,6 @@ class FakeInterestsRepository : InterestsRepository {
     private val selectedPeople = MutableStateFlow(setOf<String>())
     private val selectedPublications = MutableStateFlow(setOf<String>())
 
-    // Used to make suspend functions that read and update state safe to call from any thread
-    private val mutex = Mutex()
-
     override suspend fun getTopics(): Result<List<InterestSection>> {
         return Result.Success(topics)
     }
@@ -94,26 +90,20 @@ class FakeInterestsRepository : InterestsRepository {
     }
 
     override suspend fun toggleTopicSelection(topic: TopicSelection) {
-        mutex.withLock {
-            val set = selectedTopics.value.toMutableSet()
-            set.addOrRemove(topic)
-            selectedTopics.value = set
+        selectedTopics.update {
+            it.addOrRemove(topic)
         }
     }
 
     override suspend fun togglePersonSelected(person: String) {
-        mutex.withLock {
-            val set = selectedPeople.value.toMutableSet()
-            set.addOrRemove(person)
-            selectedPeople.value = set
+        selectedPeople.update {
+            it.addOrRemove(person)
         }
     }
 
     override suspend fun togglePublicationSelected(publication: String) {
-        mutex.withLock {
-            val set = selectedPublications.value.toMutableSet()
-            set.addOrRemove(publication)
-            selectedPublications.value = set
+        selectedPublications.update {
+            it.addOrRemove(publication)
         }
     }
 

JetNews/app/src/main/java/com/example/jetnews/data/posts/impl/BlockingFakePostsRepository.kt

@@ -25,6 +25,7 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.withContext
 
 /**
@@ -55,8 +56,6 @@ class BlockingFakePostsRepository : PostsRepository {
     override fun observeFavorites(): Flow<Set<String>> = favorites
 
     override suspend fun toggleFavorite(postId: String) {
-        val set = favorites.value.toMutableSet()
-        set.addOrRemove(postId)
-        favorites.value = set
+        favorites.update { it.addOrRemove(postId) }
     }
 }

JetNews/app/src/main/java/com/example/jetnews/data/posts/impl/FakePostsRepository.kt

@@ -22,26 +22,22 @@ import com.example.jetnews.model.Post
 import com.example.jetnews.model.PostsFeed
 import com.example.jetnews.utils.addOrRemove
 import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
-import kotlinx.coroutines.sync.Mutex
-import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.withContext
 
 /**
  * Implementation of PostsRepository that returns a hardcoded list of
  * posts with resources after some delay in a background thread.
  */
-@OptIn(ExperimentalCoroutinesApi::class)
 class FakePostsRepository : PostsRepository {
 
     // for now, store these in memory
     private val favorites = MutableStateFlow<Set<String>>(setOf())
 
     // Used to make suspend functions that read and update state safe to call from any thread
-    private val mutex = Mutex()
 
     override suspend fun getPost(postId: String?): Result<Post> {
         return withContext(Dispatchers.IO) {
@@ -68,10 +64,8 @@ class FakePostsRepository : PostsRepository {
     override fun observeFavorites(): Flow<Set<String>> = favorites
 
     override suspend fun toggleFavorite(postId: String) {
-        mutex.withLock {
-            val set = favorites.value.toMutableSet()
-            set.addOrRemove(postId)
-            favorites.value = set.toSet()
+        favorites.update {
+            it.addOrRemove(postId)
         }
     }
 

JetNews/app/src/main/java/com/example/jetnews/ui/home/HomeViewModel.kt

@@ -28,7 +28,6 @@ import com.example.jetnews.utils.ErrorMessage
 import java.util.UUID
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
-import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.flow.update
@@ -127,7 +126,7 @@ class HomeViewModel(
 
     // UI state exposed to the UI
     val uiState = viewModelState
-        .map { it.toUiState() }
+        .map(HomeViewModelState::toUiState)
         .stateIn(
             viewModelScope,
             SharingStarted.Eagerly,

JetNews/app/src/main/java/com/example/jetnews/utils/MapExtensions.kt

@@ -16,8 +16,10 @@
 
 package com.example.jetnews.utils
 
-internal fun <E> MutableSet<E>.addOrRemove(element: E) {
+internal fun <E> Set<E>.addOrRemove(element: E): Set<E> {
+    this as MutableSet
     if (!add(element)) {
         remove(element)
     }
+    return this.toSet()
 }