Implement scope-local C pointer. (#1471)

INTEROP.md

@@ -337,6 +337,22 @@ manually:
 
 In all cases the C string is supposed to be encoded as UTF-8.
 
+### Scope-local pointers ###
+
+It is possible to create scope-stable pointer of C representation of `CValues<T>`
+instance using `CValues<T>.ptr` extension property available under memScoped { ... }.
+It allows to use APIs which requires C pointers with lifetime bound to certain `MemScope`. For example:
+```
+memScoped {
+    items = arrayOfNulls<CPointer<ITEM>?>(6)
+    arrayOf("one", "two").forEachIndexed { index, value -> items[index] = value.cstr.ptr }
+    menu = new_menu("Menu".cstr.ptr, items.toCValues().ptr)
+    ...
+}
+```
+In this example all values passed to the C API `new_menu()` have lifetime of innermost `memScope`
+it belongs to. Once control flow will leave `memScoped` scope C pointers become invalid.
+
 ### Passing and receiving structs by value ###
 
 When C function takes or returns a struct `T` by value, the corresponding

Interop/Runtime/src/main/kotlin/kotlinx/cinterop/Utils.kt

@@ -412,6 +412,9 @@ class MemScope : ArenaBase() {
 
     val memScope: MemScope
         get() = this
+
+    val <T: CVariable> CValues<T>.ptr: CPointer<T>
+        get() = this@ptr.getPointer(this@MemScope)
 }
 
 // TODO: consider renaming `memScoped` because it now supports `defer`.

samples/androidNativeActivity/build.gradle

@@ -15,6 +15,7 @@ buildscript {
 
 repositories {
     jcenter()
+    google()
 }
 
 apply plugin: 'konan'
@@ -81,4 +82,4 @@ task buildApk(type: Copy) {
     dependsOn "assembleDebug"
     destinationDir outDir
     from 'build/outputs/apk'
-}
+}

samples/androidNativeActivity/src/main/kotlin/renderer.kt

@@ -306,10 +306,10 @@ class Renderer(val parentArena: NativePlacement, val nativeActivity: ANativeActi
         }
 
         glFrontFace(GL_CW)
-        glVertexPointer(4, GL_FLOAT, 0, vertices.toFloatArray().toCValues().getPointer(this))
-        glTexCoordPointer(2, GL_FLOAT, 0, texCoords.toFloatArray().toCValues().getPointer(this))
-        glNormalPointer(GL_FLOAT, 0, normals.toFloatArray().toCValues().getPointer(this))
-        glDrawElements(GL_TRIANGLES, triangles.size, GL_UNSIGNED_BYTE, triangles.toByteArray().toCValues().getPointer(this))
+        glVertexPointer(4, GL_FLOAT, 0, vertices.toFloatArray().toCValues().ptr)
+        glTexCoordPointer(2, GL_FLOAT, 0, texCoords.toFloatArray().toCValues().ptr)
+        glNormalPointer(GL_FLOAT, 0, normals.toFloatArray().toCValues().ptr)
+        glDrawElements(GL_TRIANGLES, triangles.size, GL_UNSIGNED_BYTE, triangles.toByteArray().toCValues().ptr)
 
         glPopMatrix()
 

samples/gtk/src/main/kotlin/Main.kt

@@ -54,7 +54,7 @@ fun gtkMain(args: Array<String>): Int {
     g_signal_connect(app, "activate", staticCFunction(::activate))
     val status = memScoped {
         g_application_run(app.reinterpret(),
-                args.size, args.map { it.cstr.getPointer(memScope) }.toCValues())
+                args.size, args.map { it.cstr.ptr }.toCValues())
     }
     g_object_unref(app)
     return status

samples/nonBlockingEchoServer/src/main/kotlin/EchoServer.kt

@@ -56,7 +56,7 @@ fun main(args: Array<String>) {
                 val bufferLength = 100L
                 val buffer = allocArray<ByteVar>(bufferLength)
                 val connectionIdString = "#${++connectionId}: ".cstr
-                val connectionIdBytes = connectionIdString.getPointer(this)
+                val connectionIdBytes = connectionIdString.ptr
 
                 try {
                     while (true) {
@@ -212,4 +212,4 @@ inline fun Long.ensureUnixCallResult(predicate: (Long) -> Boolean): Long {
         throw Error(getUnixError())
     }
     return this
-}
+}

samples/uikit/src/main/kotlin/main.kt

@@ -5,7 +5,7 @@ import platform.UIKit.*
 fun main(args: Array<String>) {
     memScoped {
         val argc = args.size + 1
-        val argv = (arrayOf("konan") + args).map { it.cstr.getPointer(memScope) }.toCValues()
+        val argv = (arrayOf("konan") + args).map { it.cstr.ptr }.toCValues()
 
         autoreleasepool {
             UIApplicationMain(argc, argv, null, NSStringFromClass(AppDelegate))