Add cancel function.

This should allow better stack unwinding on a fiber that
no longer needs to complete.

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Add `cancel`. Resumes a fiber but makes it immediately error at the yield point.
+- Allow multi-line paste into built in repl.
 - Add `(curenv)`.
 - Change `net/read`, `net/chunk`, and `net/write` to raise errors in the case of failures.
 - Add `janet_continue_signal` to C API. This indirectly enables C functions that yield to the event loop
@@ -16,7 +18,7 @@ All notable changes to this project will be documented in this file.
 - Expose `janet_cryptorand` in C API.
 - Properly initialize PRF in default janet program
 - Add `index-of` to core library.
-- Add `-fPIC` back to core CFLAGS (non-optional when compiling default client  with Makefile)
+- Add `-fPIC` back to core CFLAGS (non-optional when compiling default client with Makefile)
 - Fix defaults on Windows for ARM
 - Fix defaults on NetBSD.
 

src/core/asm.c

@@ -73,6 +73,7 @@ static const JanetInstructionDef janet_ops[] = {
     {"call", JOP_CALL},
     {"clo", JOP_CLOSURE},
     {"cmp", JOP_COMPARE},
+    {"cncl", JOP_CANCEL},
     {"div", JOP_DIVIDE},
     {"divim", JOP_DIVIDE_IMMEDIATE},
     {"eq", JOP_EQUALS},

src/core/bytecode.c

@@ -103,6 +103,7 @@ enum JanetInstructionType janet_instructions[JOP_INSTRUCTION_COUNT] = {
     JINT_SSS, /* JOP_NEXT */
     JINT_SSS, /* JOP_NOT_EQUALS, */
     JINT_SSI, /* JOP_NOT_EQUALS_IMMEDIATE, */
+    JINT_SSS /* JOP_CANCEL, */
 };
 
 /* Verify some bytecode */

src/core/cfuns.c

@@ -231,6 +231,9 @@ static JanetSlot do_yield(JanetFopts opts, JanetSlot *args) {
 static JanetSlot do_resume(JanetFopts opts, JanetSlot *args) {
     return opfunction(opts, args, JOP_RESUME, janet_wrap_nil());
 }
+static JanetSlot do_cancel(JanetFopts opts, JanetSlot *args) {
+    return opfunction(opts, args, JOP_CANCEL, janet_wrap_nil());
+}
 static JanetSlot do_apply(JanetFopts opts, JanetSlot *args) {
     /* Push phase */
     JanetCompiler *c = opts.compiler;
@@ -383,6 +386,7 @@ static const JanetFunOptimizer optimizers[] = {
     {fixarity2, do_modulo},
     {fixarity2, do_remainder},
     {fixarity2, do_cmp},
+    {fixarity2, do_cancel},
 };
 
 const JanetFunOptimizer *janetc_funopt(uint32_t flags) {

src/core/compile.h

@@ -61,6 +61,7 @@
 #define JANET_FUN_MODULO 29
 #define JANET_FUN_REMAINDER 30
 #define JANET_FUN_CMP 31
+#define JANET_FUN_CANCEL 32
 
 /* Compiler typedefs */
 typedef struct JanetCompiler JanetCompiler;

src/core/corelib.c

@@ -946,6 +946,10 @@ static const uint32_t resume_asm[] = {
     JOP_RESUME | (1 << 24),
     JOP_RETURN
 };
+static const uint32_t cancel_asm[] = {
+    JOP_CANCEL | (1 << 24),
+    JOP_RETURN
+};
 static const uint32_t in_asm[] = {
     JOP_IN | (1 << 24),
     JOP_LOAD_NIL | (3 << 8),
@@ -1083,6 +1087,11 @@ JanetTable *janet_core_env(JanetTable *replacements) {
                          "Yield a value to a parent fiber. When a fiber yields, its execution is paused until "
                          "another thread resumes it. The fiber will then resume, and the last yield call will "
                          "return the value that was passed to resume."));
+    janet_quick_asm(env, JANET_FUN_CANCEL,
+                    "cancel", 2, 2, 2, 2, cancel_asm, sizeof(cancel_asm),
+                    JDOC("(cancel fiber err)\n\n"
+                         "Resume a fiber but have it immediately raise an error. This lets a programmer unwind a pending fiber. "
+                         "Returns the same result as resume."));
     janet_quick_asm(env, JANET_FUN_RESUME,
                     "resume", 2, 1, 2, 2, resume_asm, sizeof(resume_asm),
                     JDOC("(resume fiber &opt x)\n\n"

src/core/vm.c

@@ -380,7 +380,7 @@ static JanetSignal run_vm(JanetFiber *fiber, Janet in) {
         &&label_JOP_NEXT,
         &&label_JOP_NOT_EQUALS,
         &&label_JOP_NOT_EQUALS_IMMEDIATE,
-        &&label_unknown_op,
+        &&label_JOP_CANCEL,
         &&label_unknown_op,
         &&label_unknown_op,
         &&label_unknown_op,
@@ -1064,6 +1064,25 @@ static JanetSignal run_vm(JanetFiber *fiber, Janet in) {
         vm_return((int) sub_status, stack[B]);
     }
 
+    VM_OP(JOP_CANCEL) {
+        Janet retreg;
+        vm_assert_type(stack[B], JANET_FIBER);
+        JanetFiber *child = janet_unwrap_fiber(stack[B]);
+        if (janet_check_can_resume(child, &retreg)) {
+            vm_commit();
+            janet_panicv(retreg);
+        }
+        fiber->child = child;
+        JanetSignal sig = janet_continue_signal(child, stack[C], &retreg, JANET_SIGNAL_ERROR);
+        if (sig != JANET_SIGNAL_OK && !(child->flags & (1 << sig))) {
+            vm_return(sig, retreg);
+        }
+        fiber->child = NULL;
+        stack = fiber->data + fiber->frame;
+        stack[A] = retreg;
+        vm_checkgc_pcnext();
+    }
+
     VM_OP(JOP_PUT)
     vm_commit();
     fiber->flags |= JANET_FIBER_RESUME_NO_USEVAL;

src/include/janet.h

@@ -1131,6 +1131,7 @@ enum JanetOpCode {
     JOP_NEXT,
     JOP_NOT_EQUALS,
     JOP_NOT_EQUALS_IMMEDIATE,
+    JOP_CANCEL,
     JOP_INSTRUCTION_COUNT
 };
 

test/suite0010.janet

@@ -44,4 +44,17 @@
 (assert (= :brackets (tuple/type (1 (macex1 '~[1 2 3 4])))) "macex1 qq bracket tuple")
 (assert (deep= (macex1 '~@[1 2 3 4 ,blah]) '~@[1 2 3 4 ,blah]) "macex1 qq array")
 
+# Cancel test
+(def f (fiber/new (fn [&] (yield 1) (yield 2) (yield 3) 4) :yti))
+(assert (= 1 (resume f)) "cancel resume 1")
+(assert (= 2 (resume f)) "cancel resume 2")
+(assert (= :hi (cancel f :hi)) "cancel resume 3")
+(assert (= :error (fiber/status f)) "cancel resume 4")
+
+# Curenv
+(assert (= (curenv) (curenv 0)) "curenv 1")
+(assert (= (table/getproto (curenv)) (curenv 1)) "curenv 2")
+(assert (= nil (curenv 1000000)) "curenv 3")
+(assert (= root-env (curenv 1)) "curenv 4")
+
 (end-suite)