new String8, String16 ctors to initialize empty static strings with static linkage

when libutils is statically linked, the ordering of the static
initializer is not guaranteed and therefore it's unsafe to use
empty static strings: e.g.:

static String8 sThisStaticStringIsNotSafe;

instead, this new constructor can be used:

static String8 sThisStaticStringIsSafe(kEmptyString);

Change-Id: Ia3daf1cab1c97d021c0ee9c2b394b5e27e8d6c0d

1 files changed, 13 insertions, 0 deletions

diff --git a/libs/utils/String16.cpp b/libs/utils/String16.cpp
index c856ceb9b2..b09b728adf 100644
--- a/libs/utils/String16.cpp
+++ b/libs/utils/String16.cpp
@@ -93,6 +93,19 @@ String16::String16()
 {
 }
 
+String16::String16(StaticLinkage)
+    : mString(0)
+{
+    // this constructor is used when we can't rely on the static-initializers
+    // having run. In this case we always allocate an empty string. It's less
+    // efficient than using getEmptyString(), but we assume it's uncommon.
+
+    char16_t* data = static_cast<char16_t*>(
+            SharedBuffer::alloc(sizeof(char16_t))->data());
+    data[0] = 0;
+    mString = data;
+}
+
 String16::String16(const String16& o)
     : mString(o.mString)
 {