These handy tips apply in any memory management situation and in any kind of IPC situation (classic Chromium IPC, Mojo, Windows/POSIX IPC, Mach IPC, files, sockets, parsing binary formats, ...).
Basically, don‘t believe the lie that ‘computers are good at arithmetic’. In general, unless you explicitly check an arithmetic operation, it’s safest to assume the operation went wrong. The least painful way to systematically check arithmetic is Chromium's base/numerics templates and helper functions.
First read about the scary security implications of integer arithmetic in C/C++. Adhere to these best practices:
uint32_t, since caller and callee could potentially use different interpretations of implicitly-sized types like
long. (For example, a 64-bit browser process and a 32-bit plug-in process might interpret
When writing code for Chromium on Android, you will often need to marshall arrays, and their sizes and indices, across the language barrier (and possibly also across the IPC barrier). The trouble here is that the Java integer types are well-defined, but the C++ integer types are whimsical. A Java
int is a signed 32-bit integer with well-defined overflow semantics, and a Java
long is a signed 64-bit integer with well-defined overflow semantics. in C++, only the explicitly-sized types (e.g.
int32_t) have guaranteed exact sizes, and only unsigned integers (of any size) have defined overflow semantics.
Essentially, Java integers actually are what people often (incorrectly) assume C++ integers are. Furthermore, Java
Arrays are indexed with Java
ints, whereas C++ arrays are indexed with
size_t (often implicitly cast, of course). Note that this also implies a 2^31 limit on the number of elements in an array that is coming from or going to Java. That Should Be Enough For Anybody, but it's good to keep in mind.
You need to make sure that every integer value survives its journey across languages intact. That generally means explicit casts with range checks; the easiest way to do this is with the
base::saturated_cast templates in base/numerics. Depending on how the integer object is going to be used, and in which direction the value is flowing, it may make sense to cast the value to
jint (an ID or regular integer),
jlong (a regular long integer),
size_t (a size or index), or one of the other more exotic C++ integer types like
Numbers have a ‘safe’ integer range of 53 bits (signed). See
charCodeAt) are unsigned 16-bit values.