Problem with a synchronization of two processes using SYSV semaphores with SEM_UNDO
I have two processes (pr. 1 and pr. 2). I want to run them in turn (1, 2, 1, 2, ..., 1, 2). I'm trying to do that using SYSV semaphores. I create two semaphores full and empty (set full = 0 and empty = 1). Than I change them in order to switch processes. Everything is OK, but there is a problem with ending (when one of the processes ends his work and dies).
I want them to wait each other, so use SEM_UNDO flag in semop (not IPC_NOWAIT). But if pr. 1 dies, SEM_UNDO returns all values it changed, so full and empty get bad values (which depends on how many times pr. 1 run). Pr. 2 gets confused and doesn't work properly.
How can I overcome this problem? Does it mean that using SEM_UNDO in some process we should not summarily change semaphore value (otherwise we will get descibed problem)?
c synchronization semaphore sysv-ipc
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
add a comment |
I have two processes (pr. 1 and pr. 2). I want to run them in turn (1, 2, 1, 2, ..., 1, 2). I'm trying to do that using SYSV semaphores. I create two semaphores full and empty (set full = 0 and empty = 1). Than I change them in order to switch processes. Everything is OK, but there is a problem with ending (when one of the processes ends his work and dies).
I want them to wait each other, so use SEM_UNDO flag in semop (not IPC_NOWAIT). But if pr. 1 dies, SEM_UNDO returns all values it changed, so full and empty get bad values (which depends on how many times pr. 1 run). Pr. 2 gets confused and doesn't work properly.
How can I overcome this problem? Does it mean that using SEM_UNDO in some process we should not summarily change semaphore value (otherwise we will get descibed problem)?
c synchronization semaphore sysv-ipc
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
add a comment |
I have two processes (pr. 1 and pr. 2). I want to run them in turn (1, 2, 1, 2, ..., 1, 2). I'm trying to do that using SYSV semaphores. I create two semaphores full and empty (set full = 0 and empty = 1). Than I change them in order to switch processes. Everything is OK, but there is a problem with ending (when one of the processes ends his work and dies).
I want them to wait each other, so use SEM_UNDO flag in semop (not IPC_NOWAIT). But if pr. 1 dies, SEM_UNDO returns all values it changed, so full and empty get bad values (which depends on how many times pr. 1 run). Pr. 2 gets confused and doesn't work properly.
How can I overcome this problem? Does it mean that using SEM_UNDO in some process we should not summarily change semaphore value (otherwise we will get descibed problem)?
c synchronization semaphore sysv-ipc
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
I have two processes (pr. 1 and pr. 2). I want to run them in turn (1, 2, 1, 2, ..., 1, 2). I'm trying to do that using SYSV semaphores. I create two semaphores full and empty (set full = 0 and empty = 1). Than I change them in order to switch processes. Everything is OK, but there is a problem with ending (when one of the processes ends his work and dies).
I want them to wait each other, so use SEM_UNDO flag in semop (not IPC_NOWAIT). But if pr. 1 dies, SEM_UNDO returns all values it changed, so full and empty get bad values (which depends on how many times pr. 1 run). Pr. 2 gets confused and doesn't work properly.
How can I overcome this problem? Does it mean that using SEM_UNDO in some process we should not summarily change semaphore value (otherwise we will get descibed problem)?
c synchronization semaphore sysv-ipc
c synchronization semaphore sysv-ipc
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
asked Nov 25 '18 at 9:14
Zyl_AlexanderZyl_Alexander
134
134
add a comment |
add a comment |
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