Source file src/runtime/debug.go

     1  // Copyright 2009 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 runtime
     6  
     7  import (
     8  	"runtime/internal/atomic"
     9  	"unsafe"
    10  )
    11  
    12  // GOMAXPROCS sets the maximum number of CPUs that can be executing
    13  // simultaneously and returns the previous setting. It defaults to
    14  // the value of runtime.NumCPU. If n < 1, it does not change the current setting.
    15  // This call will go away when the scheduler improves.
    16  func GOMAXPROCS(n int) int {
    17  	if GOARCH == "wasm" && n > 1 {
    18  		n = 1 // WebAssembly has no threads yet, so only one CPU is possible.
    19  	}
    20  
    21  	lock(&sched.lock)
    22  	ret := int(gomaxprocs)
    23  	unlock(&sched.lock)
    24  	if n <= 0 || n == ret {
    25  		return ret
    26  	}
    27  
    28  	stopTheWorldGC("GOMAXPROCS")
    29  
    30  	// newprocs will be processed by startTheWorld
    31  	newprocs = int32(n)
    32  
    33  	startTheWorldGC()
    34  	return ret
    35  }
    36  
    37  // NumCPU returns the number of logical CPUs usable by the current process.
    38  //
    39  // The set of available CPUs is checked by querying the operating system
    40  // at process startup. Changes to operating system CPU allocation after
    41  // process startup are not reflected.
    42  func NumCPU() int {
    43  	return int(ncpu)
    44  }
    45  
    46  // NumCgoCall returns the number of cgo calls made by the current process.
    47  func NumCgoCall() int64 {
    48  	var n = int64(atomic.Load64(&ncgocall))
    49  	for mp := (*m)(atomic.Loadp(unsafe.Pointer(&allm))); mp != nil; mp = mp.alllink {
    50  		n += int64(mp.ncgocall)
    51  	}
    52  	return n
    53  }
    54  
    55  // NumGoroutine returns the number of goroutines that currently exist.
    56  func NumGoroutine() int {
    57  	return int(gcount())
    58  }
    59  
    60  //go:linkname debug_modinfo runtime/debug.modinfo
    61  func debug_modinfo() string {
    62  	return modinfo
    63  }
    64  
    65  // mayMoreStackPreempt is a maymorestack hook that forces a preemption
    66  // at every possible cooperative preemption point.
    67  //
    68  // This is valuable to apply to the runtime, which can be sensitive to
    69  // preemption points. To apply this to all preemption points in the
    70  // runtime and runtime-like code, use the following in bash or zsh:
    71  //
    72  //	X=(-{gc,asm}flags={runtime/...,reflect,sync}=-d=maymorestack=runtime.mayMoreStackPreempt) GOFLAGS=${X[@]}
    73  //
    74  // This must be deeply nosplit because it is called from a function
    75  // prologue before the stack is set up and because the compiler will
    76  // call it from any splittable prologue (leading to infinite
    77  // recursion).
    78  //
    79  // Ideally it should also use very little stack because the linker
    80  // doesn't currently account for this in nosplit stack depth checking.
    81  //
    82  // Ensure mayMoreStackPreempt can be called for all ABIs.
    83  //
    84  //go:nosplit
    85  //go:linkname mayMoreStackPreempt
    86  func mayMoreStackPreempt() {
    87  	// Don't do anything on the g0 or gsignal stack.
    88  	g := getg()
    89  	if g == g.m.g0 || g == g.m.gsignal {
    90  		return
    91  	}
    92  	// Force a preemption, unless the stack is already poisoned.
    93  	if g.stackguard0 < stackPoisonMin {
    94  		g.stackguard0 = stackPreempt
    95  	}
    96  }
    97  
    98  // mayMoreStackMove is a maymorestack hook that forces stack movement
    99  // at every possible point.
   100  //
   101  // See mayMoreStackPreempt.
   102  //
   103  //go:nosplit
   104  //go:linkname mayMoreStackMove
   105  func mayMoreStackMove() {
   106  	// Don't do anything on the g0 or gsignal stack.
   107  	g := getg()
   108  	if g == g.m.g0 || g == g.m.gsignal {
   109  		return
   110  	}
   111  	// Force stack movement, unless the stack is already poisoned.
   112  	if g.stackguard0 < stackPoisonMin {
   113  		g.stackguard0 = stackForceMove
   114  	}
   115  }
   116  

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