| 5 | | Low-level implementation using malloc, linked lists and so on: |
| 6 | | |
| 7 | | {{{ |
| 8 | | |
| 9 | | #define MPI_ANY_SOURCE -1 |
| 10 | | #define MPI_ANY_TAG -2 |
| 11 | | #define MPI_INT 1 |
| 12 | | #define MPI_FLOAT 2 |
| 13 | | #define MPI_DOUBLE 3 |
| 14 | | // etc. |
| 15 | | |
| 16 | | $input int NPROCS; |
| 17 | | $assume NPROCS >= 1; |
| 18 | | $scope top; |
| 19 | | $heap mp_heap; |
| 20 | | $proc procs[NPROCS]; |
| 21 | | |
| 22 | | /* There will be one message queue for each pair of prods (i,j). |
| 23 | | * Each queue is a doubly-linked list of Message objects. |
| 24 | | */ |
| 25 | | typedef struct MPI_Message { |
| 26 | | struct MPI_Message *<top> next; |
| 27 | | struct MPI_Message *<top> prev; |
| 28 | | int tag; |
| 29 | | int size; |
| 30 | | void *<top> data; |
| 31 | | } MPI_Message; |
| 32 | | |
| 33 | | typedef struct MPI_Comm_struct { |
| 34 | | MPI_Message *<top> buf_front[NPROCS][NPROCS]; |
| 35 | | MPI_Message *<top> buf_back[NPROCS][NPROCS]; |
| 36 | | } MPI_Comm_struct; |
| 37 | | |
| 38 | | typedef MPI_Comm_struct *MPI_Comm; |
| 39 | | |
| 40 | | /* As in MPI, when a receive returns, this structure |
| 41 | | * tells you the source and tag of received message, |
| 42 | | * which you need if you used wildcards, Also size. |
| 43 | | */ |
| 44 | | typedef struct MPI_Status { |
| 45 | | int source; |
| 46 | | int tag; |
| 47 | | int size; |
| 48 | | } MPI_Status; |
| 49 | | |
| 50 | | typedef int MPI_Datatype; |
| 51 | | |
| 52 | | /* This is the actual MPI Comm world structure */ |
| 53 | | MPI_Comm_struct MPI_Comm_world_struct; |
| 54 | | |
| 55 | | /* The user will use MPI_COMM_WORLD */ |
| 56 | | MPI_Comm MPI_COMM_WORLD = &MPI_Comm_world_struct; |
| 57 | | |
| 58 | | void init() { |
| 59 | | for (int i=0; i<NPROCS; i++) |
| 60 | | procs[i] = $spawn proc(i); |
| 61 | | for (int i=0; i<NPROCS; i++) |
| 62 | | for (int j=0; j<NPROCS; j++) { |
| 63 | | MPI_COMM_WORLD->buf_front[i][j] = NULL; |
| 64 | | MPI_COMM_WORLD->buf_back[i][j] = NULL; |
| 65 | | } |
| 66 | | } |
| 67 | | |
| 68 | | int sizeofDatatype(MPI_Datatype type) { |
| 69 | | switch (type) { |
| 70 | | case MPI_INT: return sizeof(int); |
| 71 | | case MPI_FLOAT: return sizeof(float); |
| 72 | | case MPI_DOUBLE: return sizeof(double); |
| 73 | | default: exit(-1); // not yet implemented |
| 74 | | } |
| 75 | | } |
| 76 | | |
| 77 | | void MPI_process(int pid) { |
| 78 | | |
| 79 | | void MPI_Send(void *buf, int count, MPI_Datatype type, int dest, int tag, MPI_Comm comm) { |
| 80 | | // create a message |
| 81 | | Message message; |
| 82 | | |
| 83 | | message.tag = tag; |
| 84 | | message.size = count*sizeofDatatype(type); |
| 85 | | message.data = $malloc(&mp_heap, size); |
| 86 | | memcpy(message.data, buf, size); |
| 87 | | // enqueue on comm->buf_front[i][j] … |
| 88 | | // update message.next, message.prev, buf_back[i][j] |
| 89 | | } |
| 90 | | |
| 91 | | boolean match(MPI_Message *p, int source, int tag, Comm comm) { |
| 92 | | return (source == MPI_ANY_SOURCE || source == p->source) |
| 93 | | && (tag == MPI_ANY_TAG || tag == p->tag) |
| 94 | | && (comm == p->comm); |
| 95 | | } |
| 96 | | |
| 97 | | boolean probe(int source, int tag, Comm comm) { |
| 98 | | for (MPI_Message *p = comm->buf_front[source][pid]; p != NULL; p=p->next) |
| 99 | | if (match(p, source, dest, tag)) return true; |
| 100 | | return false; |
| 101 | | } |
| 102 | | |
| 103 | | boolean recv_guard(int source, int tag, Comm comm) { |
| 104 | | if (source == MPI_ANY_SOURCE) { |
| 105 | | for (int i=0; i<NPROCS; i++) { |
| 106 | | if (probe(i, tag, comm)) return true; |
| 107 | | } |
| 108 | | return false; |
| 109 | | } else { |
| 110 | | return probe(source, tag, comm); |
| 111 | | } |
| 112 | | } |
| 113 | | |
| 114 | | void recv(int dest, void *buf, int size, int source, int tag, Comm comm, Status *status) { |
| 115 | | int message_source; |
| 116 | | int message_dest; |
| 117 | | MPI_Message *message; |
| 118 | | |
| 119 | | when (recv_guard(source, tag, comm)) ; |
| 120 | | if (source == MPI_ANY_SOURCE) { |
| 121 | | for (int i=0; i<NPROCS; i++) { |
| 122 | | message = comm->buf_front[source][dest]; |
| 123 | | ... |
| 124 | | // search the queue looking for the message |
| 125 | | // also set message_source, message_dest; |
| 126 | | // and remove message from the queue |
| 127 | | } |
| 128 | | } else { |
| 129 | | … |
| 130 | | } |
| 131 | | |
| 132 | | if (message->size > size) error…; |
| 133 | | memcpy(buf, message->data, message.size); |
| 134 | | status->size = message.size; |
| 135 | | status->source = message_source; |
| 136 | | status->dest = message_dest; |
| 137 | | $free(&mp_heap, message->data); |
| 138 | | } |
| 139 | | |
| 140 | | // main body of process… |
| 141 | | |
| 142 | | $scope proc_scope; |
| 143 | | $heap proc_heap; |
| 144 | | |
| 145 | | … |
| 146 | | } |
| 147 | | |
| 148 | | void main() { |
| 149 | | for (int i=0; i<NPROCS; i++) |
| 150 | | procs[i] = $spawn(i); |
| 151 | | for (int i=0; i<NPROCS; i++) |
| 152 | | $wait procs[i]; |
| 153 | | |
| 154 | | } |
| 155 | | |
| 156 | | }}} |
| 157 | | |
| 158 | | == Second attempt == |
| 159 | | |
| 160 | | It would be much better if CIVL-C provided some abstract datatypes for message queues and so on. What should these datatypes be? Proposal: |
| | 5 | CIVL-C will provide some abstract datatypes for message queues and so on: |
