-> Anybody please explain to me, in the context below, what
-> "reentrant" means?
->
-> - The function search_binary_handler() is designed to be reentrant.
It is good to know thread-safety before knowing reentrancy.
Lot of books/papers define thread-safety and reentrancy in
different ways (sometimes incorrectly).
A function is said to be thread-safe if and only if it will
always produce correct results when called repeatedly from
multiple concurrent threads. We can identify four (nondisjoint)
classes of thread-unsafe functions:
1. Functions that do not protect shared variables
2. Functions that keep state across multiple invocations
3. Functions that return a pointer to a static variable
4. Functions that call thread-unsafe functions
Reentrant functions are an important class of thread-safe
functions, that they do not reference any shared data when
they are called by multiple threads. In other words, all
functions are partitioned into disjoint sets of thread-safe
and thread-unsafe functions. The set of reentrant functions
is a proper subset of the thread-safe functions.
Reentrant functions are more efficient than nonreentrant
thread-safe functions because they require no synchronization
operations. There are two types of reentrant functions:
1. Explicit reentrant functions
2. Implicit reentrant functions
If all function arguments are passed by value (ie. no pointers)
and all data references are to local automatic stack variables
(ie. no references to static or global variables), then the
function is explicit reentrant. That is the function is
reentrant regardless of how it is called.
If some function arguments are passed by reference (ie. we
allow callers to pass pointers) then we have an implicit
reentrant function. That function is reentrant only if the
calling threads are careful to pass pointers to nonshared
data.
Finally, it is important to realize that reentrancy is
sometimes a property of both the caller and callee, and not
only the callee alone.
So, coming to your question, we can't say whether the function
search_binary_handler() is reentrant or not without knowing
how the parameters are passed (by value or by reference) and
how it is called etc.
Venkata.
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