github.com/metacubex/gvisor@v0.0.0-20240320004321-933faba989ec/pkg/sentry/platform/systrap/subprocess_pool.go (about)

     1  // Copyright 2023 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package systrap
    16  
    17  import (
    18  	"sync"
    19  )
    20  
    21  // subprocessPool exists to solve these distinct problems:
    22  //
    23  // 1) Subprocesses can't always be killed properly (see subprocess.Release).
    24  // In general it's helpful to be able to reuse subprocesses, but we must observe
    25  // the subprocess lifecycle before we can do so (e.g. should wait for all
    26  // contexts to be released).
    27  //
    28  // 2) Any seccomp filters that have been installed will apply to subprocesses
    29  // created here. Therefore we use the intermediary (source), which is created
    30  // on initialization of the platform.
    31  type subprocessPool struct {
    32  	mu     sync.Mutex
    33  	source *subprocess
    34  	// available stores all subprocesses that are available for reuse.
    35  	// +checklocks:mu
    36  	available []*subprocess
    37  }
    38  
    39  func (p *subprocessPool) markAvailable(s *subprocess) {
    40  	p.mu.Lock()
    41  	defer p.mu.Unlock()
    42  
    43  	p.available = append(p.available, s)
    44  }
    45  
    46  func (p *subprocessPool) fetchAvailable() *subprocess {
    47  	p.mu.Lock()
    48  	defer p.mu.Unlock()
    49  	if len(p.available) > 0 {
    50  		s := p.available[len(p.available)-1]
    51  		p.available = p.available[:len(p.available)-1]
    52  
    53  		return s
    54  	}
    55  	return nil
    56  }