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Fix life.occ display buffering and ALT busy-wait #92

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Merged
associate-1 merged 1 commit into from
Feb 24, 2026
Merged

Fix life.occ display buffering and ALT busy-wait #92

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145 changes: 104 additions & 41 deletions codegen/codegen.go
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Original file line number Diff line number Diff line change
Expand Up @@ -493,6 +493,11 @@ func (g *Generator) generateEntryHarness(proc *ast.ProcDecl) {
g.writeLine(`w.WriteByte('\r')`)
g.writeLine("}")
g.writeLine("w.WriteByte(b)")
g.writeLine("if len(screen) == 0 {")
g.indent++
g.writeLine("w.Flush()")
g.indent--
g.writeLine("}")
g.indent--
g.writeLine("}")
g.indent--
Expand All @@ -519,6 +524,11 @@ func (g *Generator) generateEntryHarness(proc *ast.ProcDecl) {
g.writeLine(`w.WriteByte('\r')`)
g.writeLine("}")
g.writeLine("w.WriteByte(b)")
g.writeLine("if len(_error) == 0 {")
g.indent++
g.writeLine("w.Flush()")
g.indent--
g.writeLine("}")
g.indent--
g.writeLine("}")
g.indent--
Expand Down Expand Up @@ -1962,6 +1972,15 @@ func (g *Generator) generateAltBlock(alt *ast.AltBlock) {
}
}

// Detect guarded SKIP case — needs dual-select pattern to avoid busy-wait
guardedSkipIdx := -1
for i, c := range alt.Cases {
if c.IsSkip && c.Guard != nil {
guardedSkipIdx = i
break
}
}

if hasGuards {
// Generate channel variables for guarded cases
for i, c := range alt.Cases {
Expand All @@ -1981,55 +2000,99 @@ func (g *Generator) generateAltBlock(alt *ast.AltBlock) {
}
}

g.writeLine("select {")
for i, c := range alt.Cases {
if guardedSkipIdx >= 0 {
// Dual-select pattern: when guard is true, use default (non-blocking);
// when guard is false, omit default (blocking on channels).
g.builder.WriteString(strings.Repeat("\t", g.indent))
if c.IsSkip {
g.write("default:\n")
} else if c.IsTimer {
g.write("case <-time.After(time.Duration(")
g.generateExpression(c.Deadline)
g.write(" - int(time.Now().UnixMicro())) * time.Microsecond):\n")
} else if c.Guard != nil {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
}
g.write(fmt.Sprintf("case %s = <-_alt%d:\n", varRef, i))
} else if len(c.ChannelIndices) > 0 {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
}
g.write(fmt.Sprintf("case %s = <-%s", varRef, goIdent(c.Channel)))
g.generateIndices(c.ChannelIndices)
g.write(":\n")
} else {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
g.write("_altSkipReady := ")
g.generateExpression(alt.Cases[guardedSkipIdx].Guard)
g.write("\n")

// if _altSkipReady { select with default }
g.writeLine("if _altSkipReady {")
g.indent++
g.writeLine("select {")
for i, c := range alt.Cases {
if c.IsSkip {
g.builder.WriteString(strings.Repeat("\t", g.indent))
g.write("default:\n")
g.indent++
for _, s := range c.Body {
g.generateStatement(s)
}
g.indent--
} else {
g.generateAltChannelCase(i, c)
}
g.write(fmt.Sprintf("case %s = <-%s:\n", varRef, goIdent(c.Channel)))
}
g.writeLine("}")
g.indent--

// else { select without default — blocks on channels }
g.writeLine("} else {")
g.indent++
guardedSkip := c.IsSkip && c.Guard != nil
if guardedSkip {
g.builder.WriteString(strings.Repeat("\t", g.indent))
g.write("if ")
g.generateExpression(c.Guard)
g.write(" {\n")
g.indent++
g.writeLine("select {")
for i, c := range alt.Cases {
if !c.IsSkip {
g.generateAltChannelCase(i, c)
}
}
for _, s := range c.Body {
g.generateStatement(s)
g.writeLine("}")
g.indent--
g.writeLine("}")
} else {
// Standard single-select pattern
g.writeLine("select {")
for i, c := range alt.Cases {
if c.IsSkip {
g.builder.WriteString(strings.Repeat("\t", g.indent))
g.write("default:\n")
g.indent++
for _, s := range c.Body {
g.generateStatement(s)
}
g.indent--
} else {
g.generateAltChannelCase(i, c)
}
}
if guardedSkip {
g.indent--
g.writeLine("}")
g.writeLine("}")
}
}

// generateAltChannelCase generates a single channel or timer case for a select block.
func (g *Generator) generateAltChannelCase(i int, c ast.AltCase) {
g.builder.WriteString(strings.Repeat("\t", g.indent))
if c.IsTimer {
g.write("case <-time.After(time.Duration(")
g.generateExpression(c.Deadline)
g.write(" - int(time.Now().UnixMicro())) * time.Microsecond):\n")
} else if c.Guard != nil {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
}
g.write(fmt.Sprintf("case %s = <-_alt%d:\n", varRef, i))
} else if len(c.ChannelIndices) > 0 {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
}
g.write(fmt.Sprintf("case %s = <-%s", varRef, goIdent(c.Channel)))
g.generateIndices(c.ChannelIndices)
g.write(":\n")
} else {
varRef := goIdent(c.Variable)
if len(c.VariableIndices) > 0 {
varRef += g.generateIndicesStr(c.VariableIndices)
}
g.indent--
g.write(fmt.Sprintf("case %s = <-%s:\n", varRef, goIdent(c.Channel)))
}
g.writeLine("}")
g.indent++
for _, s := range c.Body {
g.generateStatement(s)
}
g.indent--
}

func (g *Generator) generateReplicatedAlt(alt *ast.AltBlock) {
Expand Down
32 changes: 32 additions & 0 deletions codegen/e2e_misc_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,38 @@ func TestE2E_AltGuardedSkipFalse(t *testing.T) {
}
}

func TestE2E_AltGuardedSkipFalseBlocking(t *testing.T) {
// Verify that when the SKIP guard is false, the ALT blocks on channels
// (not busy-waiting via default). The sender goes through a relay channel
// to introduce a delay, proving the ALT blocks until data arrives.
occam := `SEQ
CHAN OF INT relay:
CHAN OF INT c:
INT result:
BOOL ready:
ready := FALSE
result := 0
PAR
SEQ
ALT
ready & SKIP
result := 99
c ? result
SKIP
SEQ
INT tmp:
relay ? tmp
c ! tmp
relay ! 55
print.int(result)
`
output := transpileCompileRun(t, occam)
expected := "55\n"
if output != expected {
t.Errorf("expected %q, got %q", expected, output)
}
}

func TestE2E_MultiLineAbbreviation(t *testing.T) {
// Issue #79: IS at end of line as continuation
occam := `SEQ
Expand Down