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feat: improve maximum parallel jobs calculation close #2732 #2733

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51 changes: 41 additions & 10 deletions pkg/model/workflow.go
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Original file line number Diff line number Diff line change
@@ -1,15 +1,18 @@
package model

import (
"context"
"errors"
"fmt"
"io"
"reflect"
"regexp"
"runtime"
"strconv"
"strings"

"github.com/nektos/act/pkg/common"
"github.com/nektos/act/pkg/container"
"github.com/nektos/act/pkg/schema"
log "github.com/sirupsen/logrus"
"gopkg.in/yaml.v3"
Expand Down Expand Up @@ -210,21 +213,49 @@ type RunDefaults struct {
WorkingDirectory string `yaml:"working-directory"`
}

// GetMaxParallel sets default and returns value for `max-parallel`
// GetMaxParallel returns the maximum number of parallel jobs based on the following rules:
//
// If the user has set a MaxParallelString, parse it and return that value as-is.
//
// Otherwise, determine the limit based on the system resources by host information.
// It is assumed that each job requires 1GB of memory.
// The lower value between the number of CPU cores and total memory in GB is used as the limit.
func (s Strategy) GetMaxParallel() int {
// MaxParallel default value is `GitHub will maximize the number of jobs run in parallel depending on the available runners on GitHub-hosted virtual machines`
// So I take the liberty to hardcode default limit to 4 and this is because:
// 1: tl;dr: self-hosted does only 1 parallel job - https://github.com/actions/runner/issues/639#issuecomment-825212735
// 2: GH has 20 parallel job limit (for free tier) - https://github.com/github/docs/blob/3ae84420bd10997bb5f35f629ebb7160fe776eae/content/actions/reference/usage-limits-billing-and-administration.md?plain=1#L45
// 3: I want to add support for MaxParallel to act and 20! parallel jobs is a bit overkill IMHO
maxParallel := 4
// If the user has specified a value, try to parse and use it directly.
if s.MaxParallelString != "" {
var err error
if maxParallel, err = strconv.Atoi(s.MaxParallelString); err != nil {
val, err := strconv.Atoi(s.MaxParallelString)
if err != nil {
log.Errorf("Failed to parse 'max-parallel' option: %v", err)
} else {
return val
}
}
return maxParallel

// No user-specified value; determine system limit based on resources.
ctx := context.Background()
hostInfo, err := container.GetHostInfo(ctx)
if err != nil {
log.Errorf("Failed to retrieve host info: %v", err)
// Fallback to the number of CPU cores.
return runtime.NumCPU()
}

// Assume each job requires 1GB (1e9 bytes) of memory.
totalMemGB := int(hostInfo.MemTotal / 1e9)
cpuThreads := runtime.NumCPU()

// The system limit is the smaller of the CPU threads and total memory in GB.
sysLimit := cpuThreads
if totalMemGB < sysLimit {
sysLimit = totalMemGB
}
if sysLimit < 1 {
sysLimit = 1
}

log.Debugf("System limit for parallel jobs: %d (CPU threads: %d, Total memory: %dGB)", sysLimit, cpuThreads, totalMemGB)

return sysLimit
}

// GetFailFast sets default and returns value for `fail-fast`
Expand Down