| 1 | /*-----------------------------------------------------------------------------
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| 2 | mbx.h -- Synchronization of mailbox access
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| 3 |
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| 4 | Copyright (c) 1995 JANZ Computer AG
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| 5 | All Rights Reserved
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| 6 |
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| 7 | Created 96/01/23 by Stefan Althoefer
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| 8 | Version 1.4 of 96/07/26
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| 9 |
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| 10 | Two processes -- local and peer -- communicate via mailboxes.
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| 11 | There are two mailboxes for each direction. Thus there are four
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| 12 | mailboxes altogether referred to by indexes 0,1,2,3.
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| 13 |
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| 14 | To synchronize read-write access to the mailboxes two synchronization
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| 15 | bytes are used. These bytes are located in shared memory readable by
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| 16 | both processes. One byte is owned by the local process the other by
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| 17 | the (remote) peer process. Only the owner of a synchronization byte
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| 18 | may write it.
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| 19 |
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| 20 | There are two functions for the local process to manipulate the
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| 21 | synchronization bytes: msync_get() and msync_unget().
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| 22 | With msync_get(1) (resp. msync_get(0)) the local process requests a
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| 23 | mailbox for writing (resp. reading). The index "index" of the next box
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| 24 | ready for writing (resp. for reading) is returned. The value -1 is
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| 25 | returned if there is no such box. After using the box the local process
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| 26 | calls msync_unget(writing, index) making the box available to the peer.
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| 27 |
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| 28 | The functions are declared static. This file is meant to included in
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| 29 | the file where reading and writing mailboxes is done.
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| 30 | It is necessary to designate the send (write) direction as either
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| 31 | up or down by #defining MSYNC_UP in the local process and MSYNC_DOWN
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| 32 | in the peer process (or vice versa).
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| 33 | The addresses of the synchronization bytes must be specified
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| 34 | with MSYNC_LOCL_ADDR or MSYNC_PEER_ADDR.
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| 35 |
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| 36 | -----------------------------------------------------------------------------*/
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| 37 |
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| 38 | #ifndef mbx_DEFINED
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| 39 | #define mbx_DEFINED
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| 40 |
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| 41 | #define far
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| 42 |
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| 43 | /* Function prototypes by default */
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| 44 | #ifdef __STDC__
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| 45 | #define _PARAMS(args) args
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| 46 | #else
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| 47 | #define _PARAMS(args) ()
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| 48 | #endif
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| 49 |
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| 50 | /* Mailbox access macros */
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| 51 | #define mbx_get(i) ((unsigned char *)(MBX_BASE+(i+1) * MBX_LENGTH))
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| 52 |
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| 53 | /* Values for parameter "writing" in msync_*() */
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| 54 | #define MBX_WRITING 1
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| 55 | #define MBX_READING 0
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| 56 |
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| 57 | #define MSYNC_SHIFT(w) ((w) ? 4 : 0)
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| 58 |
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| 59 | /* Address of local synchronization byte */
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| 60 | #ifdef MSYNC_LOCL_ADDR
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| 61 | #define MSYNC_LOCL (MSYNC_LOCL_ADDR)
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| 62 | #endif
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| 63 |
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| 64 | /* Address of peer synchronization byte */
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| 65 | #ifdef MSYNC_PEER_ADDR
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| 66 | #define MSYNC_PEER (MSYNC_PEER_ADDR)
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| 67 | #endif
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| 68 |
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| 69 | #endif /* mbx_DEFINED */
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