Re: Code to behave as Re-Entrant
On 2008-09-12 08:52, Pallav singh wrote:
On Sep 12, 11:49 am, Pallav singh <singh.pal...@gmail.com> wrote:
On Sep 12, 3:35 am, juanvicfer <juanvic...@gmail.com> wrote:
On Sep 11, 7:01 pm, Erik Wikstr??m <Erik-wikst...@telia.com> wrote:
On 2008-09-11 16:11, newbar...@gmail.com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@gmail.com> wrote:
How to make flowing Code to behave as Re-Entrant ( concurrently
accessed safely by Multiple user )
Func( )
{
.
static char buffer_1 [1024] ;
/* few write Operation on buffer */
.
.
static char buffer_2 [1024] ;
/* few write Operation on buffer */
.
.
.
static char buffer_3 [1024] ;
/* few write Operation on buffer */
.
.
}- Hide quoted text -
Can you use the Boost libraries in your codebase? If so, check out the
synchronisation mechanisms in Boost.Interprocess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization_mechanisms.html).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSection().
A reentrant function is not just thread-safe, it can also safely call
iteself, which usually is not possible if the function has any static
variables.
I don??t really understand why a function with static variables usually
cannot call itself?? What I think that would happen is that that
identifier refers to the same memory position in both the caller an
the calee, right? But, where??s the problem?
--
Erik Wikstr??m
Consider a senario
we have Above code in Shared Library
user_1 has updated buffer 1 & 2 ...... He require data of either
buffer to compute for buffer 3
But i mean time user_2 start executing the function and changes data
stored in buffer 1
User_2 Corrupts Data of User_1 Un-knowingly
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A function may be non-reentrant for a number of reasons:
??? it uses a static data structure
??? it manipulates the heap: malloc(), free(), etc.
??? it uses the standard I/O library
e,g, scanf(), printf()
the library uses global data structures in a non-reentrant way
??? rely on locks to singleton resources
I fail to see why manipulating the heap would make a function non-
reentrant. If the allocator is thread-safe there is no issue, and if it
is't you can use a mutex to make the operations thread-safe.
Which of course also means that using locks to singleton resources (such
as the allocator) does not automatically make a function non-reentrant
either. On the other hand there are situations where using locks in the
wrong way can lead to problems.
--
Erik Wikstr??m
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