Hi All,
Thanks for the help.
It works now.
So, the 2 things that were required
1. Adding the '/' in front of the semaphore name so that Cygwin can
recognise it
#define SemaphoreName "/mysemaphore"
2. Changing the if check from if(semptr == (void*) -1) to if(semptr ==
(sem_t*) 0)
Thank you very much, Takashi and Corinna.
Kind Regards,
YEO Kai Wei
On 16/2/2023 10:59 pm, Corinna Vinschen wrote:
Hi Kai,
Apart from what Takashi already wrote, there's another bug in this code:
On Feb 16 12:04, Yeo Kai Wei via Cygwin wrote:
#define ByteSize 512
#define BackingFile "/shMemEx"
#define AccessPerms 0644
#define SemaphoreName "mysemaphore"
^^^^^^^^^^^^
What Takashi wrote. The reason that you don't notice that sem_open
actuially failed is...
//Create the semaphore
sem_t* semptr = sem_open( SemaphoreName,//name
O_CREAT, //create semaphore
AccessPerms, //protection permissions
0); //Initial value
//ERROR
if(semptr == (void*) -1)
^^^^^^^^^^
This.
Why do you test for -1? If you read the POSIX man page for sem_open,
you'll see this:
Upon successful completion, the sem_open() function shall return the
address of the semaphore. Otherwise, it shall return a value of
SEM_FAILED [...]
^^^^^^^^^^
SEM_FAILED is not necessarily -1. On Cygwin it's defined as
#define SEM_FAILED ((sem_t *) 0)
in /usr/include/semaphore.h.
So your code just seems to fail in sem_post, but actually that's
because sem_open failed and your code checks for the wrong return
value.
HTH,
Corinna
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