equi

commit 03f413becc8fe04d50d00b3b8d180f92e2179223
parent 080078cce5798640d8947fe1644083a69d9f6c91
Author: Luxferre <lux@ferre>
Date:   Sat, 13 Aug 2022 23:19:55 +0300

Implemented round-robin task switching mechanism

Diffstat:
M
equi.c
 | 
77
++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------------------

1 file changed, 54 insertions(+), 23 deletions(-)
diff --git a/equi.c b/equi.c
@@ -97,13 +97,14 @@ struct CLTEntry { /* one entry in the compilation lookup table */
 
 struct EquiCtx { /* one Equi program context */
   ushort id; /* task ID */
+  uchar active; /* 0 - inactive/quit, 1 - active */
+  uchar CM; /* compilation mode flag */
+  uchar IM; /* interpretation mode flag */
+  uchar lsp; /* literal stack pointer */
   ushort msp; /* main stack pointer */
   ushort rsp; /* return stack pointer */
-  ushort lsp; /* literal stack pointer */
   ushort cltp; /* compilation lookup table pointer */
   ushort cbp; /* compilation buffer pointer */
-  uchar CM; /* compilation mode flag */
-  uchar IM; /* interpretation mode flag */
   ushort gpd_start; /* GPD area start for this task */
   ushort cmd_start; /* command buffer start for this task */
   ushort cmd_size; /* size of loaded code in bytes for this task */
@@ -123,8 +124,7 @@ struct EquiRAM {
   ushort ibp; /* input buffer pointer */
   uchar II; /* instruction ignore mode flag */
   uchar MM; /* minification bypass mode flag */
-  ushort taskcount; /* count of active tasks */
-  ushort taskid; /* currently running task ID - necessary? */
+  ushort taskid; /* currently running task ID */
   struct EquiCtx tasks[EQUI_TASKS_MAX];
   uchar cmdbuf[CMD_BUF_SIZE];
 };
@@ -151,13 +151,17 @@ enum EquiErrors {
   PORT_IO_ERROR,
   PERSIST_IO_ERROR,
   RESTRICTED_WRITE_ERROR,
-  OUT_OF_BOUNDS_JUMP
+  OUT_OF_BOUNDS_JUMP,
+  TASK_SLOTS_FULL
 };
 
 /* Error reporting method */
 void trapout(errcode) {
   if(errcode > 0) {
-    fprintf(stderr, "\nError %d at 0x%x (task 0x%x, instruction %c): ", errcode, curtask->pc, curtask->id, flatram[curtask->pc]);
+    if(curtask)
+      fprintf(stderr, "\nError %d at 0x%x (task 0x%x, instruction %c): ", errcode, curtask->pc, curtask->id, flatram[curtask->pc]);
+    else
+      fprintf(stderr, "\nSystem error %d: ", errcode);
     switch(errcode) {
       case STACK_OVERFLOW:
         cerr("Stack overflow\n");
@@ -192,6 +196,9 @@ void trapout(errcode) {
       case OUT_OF_BOUNDS_JUMP:
         cerr("Attempt to jump outside the task context\n");
         break;
+      case TASK_SLOTS_FULL:
+        cerr("All task slots busy and active\n");
+        break;
     }
     exit(errcode);
   }
@@ -391,18 +398,43 @@ void portIO(ushort port, ushort p2, ushort p1) {
   pushMain(status);
 }
 
+/* end of internal helper functions, start of main Equi functions */
+
+/* Find free task slot among remaining inactive tasks */
+ushort equi_find_free_task_slot() {
+  ushort slotid = 0;
+  /* iterate over task table */
+  for(;slotid < EQUI_TASKS_MAX;slotid++)
+    if(!ram.tasks[slotid].active)
+      return slotid;
+  /* and error out if all slots are busy and active */
+  trapout(TASK_SLOTS_FULL);
+  return TASK_SLOTS_FULL;
+}
+
+/* Find the next active task in the table, round-robin fashion */
+struct EquiCtx* equi_find_next_task() {
+  ushort oldtaskid = ram.taskid; /* save the current one to avoid deadlocks */
+  while(!ram.tasks[ram.taskid].active) {
+    ++ram.taskid;
+    if(ram.taskid == EQUI_TASKS_MAX) ram.taskid = 0;
+    if(ram.taskid == oldtaskid) /* found no active tasks, bailing out */
+      return NULL;
+  }
+  return &ram.tasks[ram.taskid];
+}
+
 /* Task loader method */
 struct EquiCtx* equi_load_task(ushort progStart, ushort len) {
-  struct EquiCtx *taskptr = &ram.tasks[ram.taskcount]; /* refer to the last available entry */
+  ushort tid = equi_find_free_task_slot();
+  struct EquiCtx *taskptr = &ram.tasks[tid]; /* refer to the next available entry */
   taskptr->msp = taskptr->rsp = taskptr->lsp = taskptr->cltp = 0; /* init stacks and CLT */
   taskptr->pc = progStart - 1U; /* init program counter for preincrement logic */
   taskptr->cmd_start = progStart; /* actual command buffer start (from the start of vRAM) */
   taskptr->cmd_size = len; /* actual command buffer size */
-  taskptr->id = ram.taskcount; /* assign task ID */
+  taskptr->id = tid; /* assign task ID */
   taskptr->gpd_start = (ushort) (taskptr->gpd - flatram); /* assign GPD area start */
-  taskptr->IM = 1; /* set interpretation mode flag */
   taskptr->CM = 0; /* unset compilation mode flag */
-  ++ram.taskcount; /* increase task count */
   return taskptr;
 }
 
@@ -413,9 +445,12 @@ void equi_main_loop() {
   /* try to open the persistent sandbox file */
   FILE *pfd = fopen(PERSIST_FILE, "r+b");
   while(1) { /* iterate over the instructions in the command buffer */
+    curtask = equi_find_next_task(); /* attempt to switch the context on every iteration */
+    if(curtask == NULL) break; /* exit the main loop when no tasks are left */
     instr = flatram[++curtask->pc];
     /* silently exit on zero or FF */
-    if(instr == 0 || instr == 0xFFu) break;
+    if(instr == 0 || instr == 0xFFu)
+      curtask->active = 0;
     /* first, check for II mode */
     if(ram.II) {
       if(instr == INS_IIEND)
@@ -458,8 +493,9 @@ void equi_main_loop() {
       case '\t':
       case ' ': /* all nops in interpretation mode */
         break;
-      case INS_QUIT: /* gracefully quit the interpretation mode */
-        goto brx;
+      case INS_QUIT: /* gracefully quit the task */
+        curtask->active = 0;
+        break;
       case INS_LITINT: /* literal stack -> main stack as short */
         pushLitVal();
         break;
@@ -622,20 +658,14 @@ void equi_main_loop() {
         break;
       default: /* all characters not processed before are invalid instructions */
         trapout(INVALID_INSTRUCTION);
-        goto brx;
     }
     if(curtask->msp >= STACK_SIZE_WORDS || curtask->rsp >= STACK_SIZE_WORDS) /* check for stack overflow after any operation */
       trapout(STACK_OVERFLOW);
-    continue;
-    brx: break;
   }
   /* close the persistent sandbox file if open */
   if(pfd) fclose(pfd);
-  /* unset interpretation mode flag and exit */
-  curtask->IM = 0;
-  curtask->pc = ram.ibp = 65535U;
-  /* clear all stacks and CLT */
-  curtask->msp = curtask->rsp = curtask->lsp = curtask->cltp = 0;
+  /* reset IBP and exit */
+  ram.ibp = 65535U;
 }
 
 /* Equi VM entry point */
@@ -657,7 +687,6 @@ int main(int argc, char* argv[]) {
   ram.cmd_start = (uchar *)&ram.cmdbuf - (uchar *)&ram;
   ram.cmd_size = CMD_BUF_SIZE;
   ram.II = ram.MM = 0; /* reset all flags */
-  ram.taskcount = 0;
   /* process command line params */
   if(argc > 1 && argv[1][0] == 'm') /* enter minification mode, don't run the programs */
     ram.MM = 1;
@@ -709,6 +738,8 @@ int main(int argc, char* argv[]) {
         }
         ram.cmdbuf[++ram.ibp] = INS_QUIT; /* end program with INS_QUIT */
         curtask = equi_load_task((ushort)ram.cmd_start, ram.ibp + 1); /* load the code as task 0 */
+        ram.taskid = curtask->id; /* actualize the current task id */
+        curtask->active = 1; /*activate the current task */
         equi_main_loop(); /* and run the interpreter loop */
         if(!smode) {
           cputc(CR); /* echo CR */