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 */
..
..
}
8  1883 
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
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.Interproc ess ( http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
Regards,
Pete
On 2008-09-11 16:11, ne*******@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
>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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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.
--
Erik Wikström
On 2008-09-11 12:21, Pallav singh 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 */
.
.
}
Make the buffers non-static, of if that grows to much on the stack
allocate the buffers dynamically. Also you should investigate the
possibility to only use one buffer.
--
Erik Wikström
On Sep 11, 7:01*pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-11 16:11, newbar...@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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 Wikström
On Sep 12, 3:35*am, juanvicfer <juanvic...@gma il.comwrote:
On Sep 11, 7:01*pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-11 16:11, newbar...@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
>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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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 Wikström
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
On Sep 12, 11:49*am, Pallav singh <singh.pal...@g mail.comwrote:
On Sep 12, 3:35*am, juanvicfer <juanvic...@gma il.comwrote:
On Sep 11, 7:01*pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-11 16:11, newbar...@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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 Wikström
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
IO code is usually not reentrant because it relies on shared,
singleton resources such as disks.
On 2008-09-12 08:52, Pallav singh wrote:
On Sep 12, 11:49 am, Pallav singh <singh.pal...@g mail.comwrote:
>On Sep 12, 3:35 am, juanvicfer <juanvic...@gma il.comwrote:
On Sep 11, 7:01 pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-11 16:11, newbar...@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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 Wikström
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 Wikström
On Sep 12, 5:48 pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-12 08:52, Pallav singh wrote:
On Sep 12, 11:49 am, Pallav singh <singh.pal...@g mail.comwrote:
On Sep 12, 3:35 am, juanvicfer <juanvic...@gma il.comwrote:
On Sep 11, 7:01 pm, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2008-09-11 16:11, newbar...@gmail .com wrote:
On 11 Sep, 11:21, Pallav singh <singh.pal...@g mail.comwrote:
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.Interproc ess (http://www.boost.org/
doc/libs/1_36_0/doc/html/interprocess/
synchronization _mechanisms.htm l).
Alternatively, are you on Win32? Take a look at the WINAPI call
EnterCriticalSe ction().
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 Wikström
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.
Well, reentrancy is a stronger property than thread safety. For
example under posix, a function execution can be interrupted at any
point by a signal which causes the execution of the signal handler.
Protecting the shared state between the interrupted function and the
handler by a mutex is not necessary nor sufficient to guarantee
reentrancy. Posix calls this type of reentrancy async signal safety.
Memory allocation is not async signal safe. This is beyond standard C+
+, though.
--
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