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[JSC] Make CodeBlock old-age TTL configurable via Options #229

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[JSC] Make CodeBlock old-age TTL configurable via Options #229

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8 changes: 4 additions & 4 deletions Source/JavaScriptCore/bytecode/CodeBlock.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1282,15 +1282,15 @@ static Seconds NODELETE timeToLive(JITType jitType)

switch (jitType) {
case JITType::InterpreterThunk:
return 5_s;
return Seconds(Options::interpreterThunkTimeToLiveSeconds());
case JITType::BaselineJIT:
// Effectively 10 additional seconds, since BaselineJIT and
// InterpreterThunk share a CodeBlock.
return 15_s;
return Seconds(Options::baselineJITTimeToLiveSeconds());
case JITType::DFGJIT:
return 20_s;
return Seconds(Options::dfgJITTimeToLiveSeconds());
case JITType::FTLJIT:
return 60_s;
return Seconds(Options::ftlJITTimeToLiveSeconds());
Comment on lines +1285 to +1293
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@coderabbitai coderabbitai Bot May 14, 2026

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⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Sanitize configurable TTL values before constructing Seconds.

These values are externally configurable; negative/invalid inputs can force immediate old-age jettison and create unnecessary recompile churn. Clamp at the call site.

Suggested fix 
 static Seconds NODELETE timeToLive(JITType jitType)
 {
+    auto sanitizeTTL = [] (double seconds) -> Seconds {
+        return Seconds(seconds >= 0 ? seconds : 0);
+    };
+
     if (Options::useEagerCodeBlockJettisonTiming()) [[unlikely]] {
         switch (jitType) {
         case JITType::InterpreterThunk:
             return 10_ms;
@@
     switch (jitType) {
     case JITType::InterpreterThunk:
-        return Seconds(Options::interpreterThunkTimeToLiveSeconds());
+        return sanitizeTTL(Options::interpreterThunkTimeToLiveSeconds());
     case JITType::BaselineJIT:
         // Effectively 10 additional seconds, since BaselineJIT and
         // InterpreterThunk share a CodeBlock.
-        return Seconds(Options::baselineJITTimeToLiveSeconds());
+        return sanitizeTTL(Options::baselineJITTimeToLiveSeconds());
     case JITType::DFGJIT:
-        return Seconds(Options::dfgJITTimeToLiveSeconds());
+        return sanitizeTTL(Options::dfgJITTimeToLiveSeconds());
     case JITType::FTLJIT:
-        return Seconds(Options::ftlJITTimeToLiveSeconds());
+        return sanitizeTTL(Options::ftlJITTimeToLiveSeconds());
     default:
         return Seconds::infinity();
     }
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
return Seconds(Options::interpreterThunkTimeToLiveSeconds());
case JITType::BaselineJIT:
// Effectively 10 additional seconds, since BaselineJIT and
// InterpreterThunk share a CodeBlock.
return 15_s;
return Seconds(Options::baselineJITTimeToLiveSeconds());
case JITType::DFGJIT:
return 20_s;
return Seconds(Options::dfgJITTimeToLiveSeconds());
case JITType::FTLJIT:
return 60_s;
return Seconds(Options::ftlJITTimeToLiveSeconds());
static Seconds NODELETE timeToLive(JITType jitType)
{
auto sanitizeTTL = [] (double seconds) -> Seconds {
return Seconds(seconds >= 0 ? seconds : 0);
};
if (Options::useEagerCodeBlockJettisonTiming()) [[unlikely]] {
switch (jitType) {
case JITType::InterpreterThunk:
return 10_ms;
case JITType::BaselineJIT:
return 100_ms;
case JITType::DFGJIT:
return 1_s;
case JITType::FTLJIT:
return 10_s;
default:
ASSERT_NOT_REACHED();
}
}
switch (jitType) {
case JITType::InterpreterThunk:
return sanitizeTTL(Options::interpreterThunkTimeToLiveSeconds());
case JITType::BaselineJIT:
// Effectively 10 additional seconds, since BaselineJIT and
// InterpreterThunk share a CodeBlock.
return sanitizeTTL(Options::baselineJITTimeToLiveSeconds());
case JITType::DFGJIT:
return sanitizeTTL(Options::dfgJITTimeToLiveSeconds());
case JITType::FTLJIT:
return sanitizeTTL(Options::ftlJITTimeToLiveSeconds());
default:
return Seconds::infinity();
}
}
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@Source/JavaScriptCore/bytecode/CodeBlock.cpp` around lines 1285 - 1293, The
TTL values returned from Options (used in the switch over JITType in
CodeBlock.cpp) must be sanitized before constructing Seconds to avoid
negative/invalid inputs causing immediate eviction; for each case
(InterpreterThunk, BaselineJIT, DFGJIT, FTLJIT) read the raw config value from
Options::*, clamp it to a safe non-negative range (e.g. using std::max(0, value)
or std::clamp(value, 0, someUpperBound)) and then construct and return
Seconds(clampedValue) instead of passing the raw value directly to Seconds.
Ensure you adjust the InterpreterThunk, BaselineJIT, DFGJIT and FTLJIT return
sites accordingly.

default:
return Seconds::infinity();
}
Expand Down
4 changes: 4 additions & 0 deletions Source/JavaScriptCore/runtime/OptionsList.h
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Original file line number Diff line number Diff line change
Expand Up @@ -436,6 +436,10 @@ bool hasCapacityToUseLargeGigacage();
v(Bool, dumpHeapOnLowMemory, false, Normal, "Dump a heap dump when the memory handler is triggered. Use alongside $vm.triggerMemoryPressure() and enableStrongRefTracker."_s) \
v(Bool, forceCodeBlockToJettisonDueToOldAge, false, Normal, "If true, this means that anytime we can jettison a CodeBlock due to old age, we do."_s) \
v(Bool, useEagerCodeBlockJettisonTiming, false, Normal, "If true, the time slices for jettisoning a CodeBlock due to old age are shrunk significantly."_s) \
v(Double, interpreterThunkTimeToLiveSeconds, 5.0, Normal, "Seconds before an InterpreterThunk CodeBlock is eligible for old-age jettison."_s) \
v(Double, baselineJITTimeToLiveSeconds, 15.0, Normal, "Seconds before a BaselineJIT CodeBlock is eligible for old-age jettison."_s) \
v(Double, dfgJITTimeToLiveSeconds, 20.0, Normal, "Seconds before a DFGJIT CodeBlock is eligible for old-age jettison."_s) \
v(Double, ftlJITTimeToLiveSeconds, 60.0, Normal, "Seconds before an FTLJIT CodeBlock is eligible for old-age jettison."_s) \
\
v(Bool, useTypeProfiler, false, Normal, nullptr) \
v(Bool, useControlFlowProfiler, false, Normal, nullptr) \
Expand Down
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