cutils: add ashmem_init

Add a new ashmem_init function that only dlopens libashmemd_client.
This allows the library to be preloaded in the zygote.

Test: boots, works
Bug: 129543489

Change-Id: Ie106791edf381654f085203c266c9f9c0df35cfc
diff --git a/libcutils/ashmem-dev.cpp b/libcutils/ashmem-dev.cpp
index e35b91a..e67b458 100644
--- a/libcutils/ashmem-dev.cpp
+++ b/libcutils/ashmem-dev.cpp
@@ -73,6 +73,8 @@
 #ifndef __ANDROID_VNDK__
 using openFdType = int (*)();
 
+static openFdType openFd;
+
 openFdType initOpenAshmemFd() {
     openFdType openFd = nullptr;
     void* handle = dlopen("libashmemd_client.so", RTLD_NOW);
@@ -221,7 +223,10 @@
 
     int fd = -1;
 #ifndef __ANDROID_VNDK__
-    static auto openFd = initOpenAshmemFd();
+    if (!openFd) {
+        openFd = initOpenAshmemFd();
+    }
+
     if (openFd) {
         fd = openFd();
     }
@@ -480,3 +485,11 @@
 
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_GET_SIZE, NULL)));
 }
+
+void ashmem_init() {
+#ifndef __ANDROID_VNDK__
+    pthread_mutex_lock(&__ashmem_lock);
+    openFd = initOpenAshmemFd();
+    pthread_mutex_unlock(&__ashmem_lock);
+#endif  //__ANDROID_VNDK__
+}