problem implementing fork


 
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Old 10-11-2009
A couple of things come to mnd....
  1. I'd use something other than SIGALRM to signal the parent. Perhaps SIGCHLD or SIGUSR1
  2. Forking gives the parent the opportunity to do something useful if the kid hangs. For instance, if the I/O subsystem were to be unable to complete an i/o and fail to return an error on a Solaris (or any system using DMA for I/O) , the kid will be unkillable and hang. This is because you might remove the process memory, reallocate it to another process only to have the DMA device complete the physical i/o. It might be useful to tell someone about the i/o issue via a timeout mechanism.
  3. Is forking all that expensive in a Linux system? Most everything except for the LWP stuff will be created with either model. The forking model makes expansion of the code to handle multiple tasks saner..

sorry about the late reply...
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FORK(2) 							System Calls Manual							   FORK(2)

NAME
fork - spawn new process SYNOPSIS
fork( ) DESCRIPTION
Fork is the only way new processes are created. The new process's core image is a copy of that of the caller of fork. The only distinc- tion is the fact that the value returned in the old (parent) process contains the process ID of the new (child) process, while the value returned in the child is 0. Process ID's range from 1 to 30,000. This process ID is used by wait(2). Files open before the fork are shared, and have a common read-write pointer. In particular, this is the way that standard input and output files are passed and also how pipes are set up. SEE ALSO
wait(2), exec(2) DIAGNOSTICS
Returns -1 and fails to create a process if: there is inadequate swap space, the user is not super-user and has too many processes, or the system's process table is full. Only the super-user can take the last process-table slot. ASSEMBLER
(fork = 2.) sys fork (new process return) (old process return, new process ID in r0) The return locations in the old and new process differ by one word. The C-bit is set in the old process if a new process could not be cre- ated. FORK(2)