checkfinalizers.go

     1  // Copyright 2024 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package main
     6  
     7  import (
     8  	"internal/asan"
     9  	"internal/race"
    10  	"runtime"
    11  	"runtime/debug"
    12  	"unsafe"
    13  )
    14  
    15  func init() {
    16  	register("DetectFinalizerAndCleanupLeaks", DetectFinalizerAndCleanupLeaks)
    17  }
    18  
    19  type tiny uint8
    20  
    21  var tinySink *tiny
    22  
    23  // Intended to be run only with `GODEBUG=checkfinalizers=1`.
    24  func DetectFinalizerAndCleanupLeaks() {
    25  	type T *int
    26  
    27  	defer debug.SetGCPercent(debug.SetGCPercent(-1))
    28  
    29  	// Leak a cleanup.
    30  	cLeak := new(T)
    31  	runtime.AddCleanup(cLeak, func(x int) {
    32  		**cLeak = x
    33  	}, int(0))
    34  
    35  	// Have a regular cleanup to make sure it doesn't trip the detector.
    36  	cNoLeak := new(T)
    37  	runtime.AddCleanup(cNoLeak, func(_ int) {}, int(0))
    38  
    39  	// Add a cleanup that only temporarily leaks cNoLeak.
    40  	runtime.AddCleanup(cNoLeak, func(x int) {
    41  		**cNoLeak = x
    42  	}, int(0)).Stop()
    43  
    44  	if !asan.Enabled && !race.Enabled {
    45  		// Ensure we create an allocation into a tiny block that shares space among several values.
    46  		//
    47  		// Don't do this with ASAN and in race mode, where the tiny allocator is disabled.
    48  		// We might just loop forever here in that case.
    49  		var ctLeak *tiny
    50  		for {
    51  			tinySink = ctLeak
    52  			ctLeak = new(tiny)
    53  			*ctLeak = tiny(55)
    54  			// Make sure the address is an odd value. This is sufficient to
    55  			// be certain that we're sharing a block with another value and
    56  			// trip the detector.
    57  			if uintptr(unsafe.Pointer(ctLeak))%2 != 0 {
    58  				break
    59  			}
    60  		}
    61  		runtime.AddCleanup(ctLeak, func(_ struct{}) {}, struct{}{})
    62  	}
    63  
    64  	// Leak a finalizer.
    65  	fLeak := new(T)
    66  	runtime.SetFinalizer(fLeak, func(_ *T) {
    67  		**fLeak = 12
    68  	})
    69  
    70  	// Have a regular finalizer to make sure it doesn't trip the detector.
    71  	fNoLeak := new(T)
    72  	runtime.SetFinalizer(fNoLeak, func(x *T) {
    73  		**x = 51
    74  	})
    75  
    76  	// runtime.GC here should crash.
    77  	runtime.GC()
    78  	println("OK")
    79  }
    80
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