allow fast flicking through any list panel

Up till now our approach to rendering things like file diffs, branch logs, and
commit patches, has been to run a command on the command line, wait for it to
complete, take its output as a string, and then write that string to the main
view (or secondary view e.g. when showing both staged and unstaged changes of a
file).

This has caused various issues. For once, if you are flicking through a list of
files and an untracked file is particularly large, not only will this require
lazygit to load that whole file into memory (or more accurately it's equally
large diff), it also will slow down the UI thread while loading that file, and
if the user continued down the list, the original command might eventually
resolve and replace whatever the diff is for the newly selected file.

Following what we've done in lazydocker, I've added a tasks package for when you
need something done but you want it to cancel as soon as something newer comes
up. Given this typically involves running a command to display to a view, I've
added a viewBufferManagerMap struct to the Gui struct which allows you to define
these tasks on a per-view basis.

viewBufferManagers can run files and directly write the output to their view,
meaning we no longer need to use so much memory.

In the tasks package there is a helper method called NewCmdTask which takes a
command, an initial amount of lines to read, and then runs that command, reads
that number of lines, and allows for a readLines channel to tell it to read more
lines. We read more lines when we scroll or resize the window.

There is an adapter for the tasks package in a file called tasks_adapter which
wraps the functions from the tasks package in gui-specific stuff like clearing
the main view before starting the next task that wants to write to the main
view.

I've removed some small features as part of this work, namely the little headers
that were at the top of the main view for some situations. For example, we no
longer show the upstream of a selected branch. I want to re-introduce this in
the future, but I didn't want to make this tasks system too complicated, and in
order to facilitate a header section in the main view we'd need to have a task
that gets the upstream for the current branch, writes it to the header, then
tells another task to write the branch log to the main view, but without
clearing inbetween. So it would get messy. I'm thinking instead of having a
separate 'header' view atop the main view to render that kind of thing (which
can happen in another PR)

I've also simplified the 'git show' to just call 'git show' and not do anything
fancy when it comes to merge commits.

I considered using this tasks approach whenever we write to a view. The only
thing is that the renderString method currently resets the origin of a view and
I don't want to lose that. So I've left some in there that I consider harmless,
but we should probably be just using tasks now for all rendering, even if it's
just strings we can instantly make.

16 files changed, 490 insertions, 244 deletions

diff --git a/pkg/commands/git.go b/pkg/commands/git.go
index f72280d64..fb4ddab79 100644
--- a/pkg/commands/git.go
+++ b/pkg/commands/git.go
@@ -176,8 +176,8 @@ func stashEntryFromLine(line string, index int) *StashEntry {
 }
 
 // GetStashEntryDiff stash diff
-func (c *GitCommand) GetStashEntryDiff(index int) (string, error) {
-	return c.OSCommand.RunCommandWithOutput("git stash show -p --color stash@{%d}", index)
+func (c *GitCommand) ShowStashEntryCmdStr(index int) string {
+	return fmt.Sprintf("git stash show -p --color stash@{%d}", index)
 }
 
 // GetStatusFiles git status files
@@ -538,7 +538,8 @@ func (c *GitCommand) PrepareCommitAmendSubProcess() *exec.Cmd {
 // Currently it limits the result to 100 commits, but when we get async stuff
 // working we can do lazy loading
 func (c *GitCommand) GetBranchGraph(branchName string) (string, error) {
-	return c.OSCommand.RunCommandWithOutput("git log --graph --color --abbrev-commit --decorate --date=relative --pretty=medium -100 %s", branchName)
+	cmdStr := c.GetBranchGraphCmdStr(branchName)
+	return c.OSCommand.RunCommandWithOutput(cmdStr)
 }
 
 func (c *GitCommand) GetUpstreamForBranch(branchName string) (string, error) {
@@ -551,41 +552,12 @@ func (c *GitCommand) Ignore(filename string) error {
 	return c.OSCommand.AppendLineToFile(".gitignore", filename)
 }
 
-// Show shows the diff of a commit
-func (c *GitCommand) Show(sha string) (string, error) {
-	show, err := c.OSCommand.RunCommandWithOutput("git show --color --no-renames %s", sha)
-	if err != nil {
-		return "", err
-	}
-
-	// if this is a merge commit, we need to go a step further and get the diff between the two branches we merged
-	revList, err := c.OSCommand.RunCommandWithOutput("git rev-list -1 --merges %s^...%s", sha, sha)
-	if err != nil {
-		// turns out we get an error here when it's the first commit. We'll just return the original show
-		return show, nil
-	}
-	if len(revList) == 0 {
-		return show, nil
-	}
-
-	// we want to pull out 1a6a69a and 3b51d7c from this:
-	// commit ccc771d8b13d5b0d4635db4463556366470fd4f6
-	// Merge: 1a6a69a 3b51d7c
-	lines := utils.SplitLines(show)
-	if len(lines) < 2 {
-		return show, nil
-	}
-
-	secondLineWords := strings.Split(lines[1], " ")
-	if len(secondLineWords) < 3 {
-		return show, nil
-	}
+func (c *GitCommand) ShowCmdStr(sha string) string {
+	return fmt.Sprintf("git show --color --no-renames %s", sha)
+}
 
-	mergeDiff, err := c.OSCommand.RunCommandWithOutput("git diff --color %s...%s", secondLineWords[1], secondLineWords[2])
-	if err != nil {
-		return "", err
-	}
-	return show + mergeDiff, nil
+func (c *GitCommand) GetBranchGraphCmdStr(branchName string) string {
+	return fmt.Sprintf("git log --graph --color --abbrev-commit --decorate --date=relative --pretty=medium %s", branchName)
 }
 
 // GetRemoteURL returns current repo remote url
@@ -606,6 +578,12 @@ func (c *GitCommand) CheckRemoteBranchExists(branch *Branch) bool {
 
 // Diff returns the diff of a file
 func (c *GitCommand) Diff(file *File, plain bool, cached bool) string {
+	// for now we assume an error means the file was deleted
+	s, _ := c.OSCommand.RunCommandWithOutput(c.DiffCmdStr(file, plain, cached))
+	return s
+}
+
+func (c *GitCommand) DiffCmdStr(file *File, plain bool, cached bool) string {
 	cachedArg := ""
 	trackedArg := "--"
 	colorArg := "--color"
@@ -621,9 +599,7 @@ func (c *GitCommand) Diff(file *File, plain bool, cached bool) string {
 		colorArg = ""
 	}
 
-	// for now we assume an error means the file was deleted
-	s, _ := c.OSCommand.RunCommandWithOutput("git diff %s %s %s %s", colorArg, cachedArg, trackedArg, fileName)
-	return s
+	return fmt.Sprintf("git diff %s %s %s %s", colorArg, cachedArg, trackedArg, fileName)
 }
 
 func (c *GitCommand) ApplyPatch(patch string, flags ...string) error {
@@ -908,11 +884,17 @@ func (c *GitCommand) GetCommitFiles(commitSha string, patchManager *PatchManager
 
 // ShowCommitFile get the diff of specified commit file
 func (c *GitCommand) ShowCommitFile(commitSha, fileName string, plain bool) (string, error) {
+	cmdStr := c.ShowCommitFileCmdStr(commitSha, fileName, plain)
+	return c.OSCommand.RunCommandWithOutput(cmdStr)
+}
+
+func (c *GitCommand) ShowCommitFileCmdStr(commitSha, fileName string, plain bool) string {
 	colorArg := "--color"
 	if plain {
 		colorArg = ""
 	}
-	return c.OSCommand.RunCommandWithOutput("git show --no-renames %s %s -- %s", colorArg, commitSha, fileName)
+
+	return fmt.Sprintf("git show --no-renames %s %s -- %s", colorArg, commitSha, fileName)
 }
 
 // CheckoutFile checks out the file for the given commit
@@ -1098,10 +1080,6 @@ func (c *GitCommand) CreateLightweightTag(tagName string, commitSha string) erro
 	return c.OSCommand.RunCommand("git tag %s %s", tagName, commitSha)
 }
 
-func (c *GitCommand) ShowTag(tagName string) (string, error) {
-	return c.OSCommand.RunCommandWithOutput("git tag -n99 %s", tagName)
-}
-
 func (c *GitCommand) DeleteTag(tagName string) error {
 	return c.OSCommand.RunCommand("git tag -d %s", tagName)
 }
diff --git a/pkg/commands/git_test.go b/pkg/commands/git_test.go
index 0429165de..ceaadc576 100644
--- a/pkg/commands/git_test.go
+++ b/pkg/commands/git_test.go
@@ -318,21 +318,6 @@ func TestGitCommandGetStashEntries(t *testing.T) {
 	}
 }
 
-// TestGitCommandGetStashEntryDiff is a function.
-func TestGitCommandGetStashEntryDiff(t *testing.T) {
-	gitCmd := NewDummyGitCommand()
-	gitCmd.OSCommand.command = func(cmd string, args ...string) *exec.Cmd {
-		assert.EqualValues(t, "git", cmd)
-		assert.EqualValues(t, []string{"stash", "show", "-p", "--color", "stash@{1}"}, args)
-
-		return exec.Command("echo")
-	}
-
-	_, err := gitCmd.GetStashEntryDiff(1)
-
-	assert.NoError(t, err)
-}
-
 // TestGitCommandGetStatusFiles is a function.
 func TestGitCommandGetStatusFiles(t *testing.T) {
 	type scenario struct {
@@ -1411,66 +1396,6 @@ func TestGitCommandDiscardAllFileChanges(t *testing.T) {
 	}
 }
 
-// TestGitCommandShow is a function.
-func TestGitCommandShow(t *testing.T) {
-	type scenario struct {
-		testName string
-		arg      string
-		command  func(string, ...string) *exec.Cmd
-		test     func(string, error)
-	}
-
-	scenarios := []scenario{
-		{
-			"regular commit",
-			"456abcde",
-			test.CreateMockCommand(t, []*test.CommandSwapper{
-				{
-					Expect:  "git show --color --no-renames 456abcde",
-					Replace: "echo \"commit ccc771d8b13d5b0d4635db4463556366470fd4f6\nblah\"",
-				},
-				{
-					Expect:  "git rev-list -1 --merges 456abcde^...456abcde",
-					Replace: "echo",
-				},
-			}),
-			func(result string, err error) {
-				assert.NoError(t, err)
-				assert.Equal(t, "commit ccc771d8b13d5b0d4635db4463556366470fd4f6\nblah\n", result)
-			},
-		},
-		{
-			"merge commit",
-			"456abcde",
-			test.CreateMockCommand(t, []*test.CommandSwapper{
-				{
-					Expect:  "git show --color --no-renames 456abcde",
-					Replace: "echo \"commit ccc771d8b13d5b0d4635db4463556366470fd4f6\nMerge: 1a6a69a 3b51d7c\"",
-				},
-				{
-					Expect:  "git rev-list -1 --merges 456abcde^...456abcde",
-					Replace: "echo aa30e006433628ba9281652952b34d8aacda9c01",
-				},
-				{
-					Expect:  "git diff --color 1a6a69a...3b51d7c",
-					Replace: "echo blah",
-				},
-			}),
-			func(result string, err error) {
-				assert.NoError(t, err)
-				assert.Equal(t, "commit ccc771d8b13d5b0d4635db4463556366470fd4f6\nMerge: 1a6a69a 3b51d7c\nblah\n", result)
-			},
-		},
-	}
-
-	gitCmd := NewDummyGitCommand()
-
-	for _, s := range scenarios {
-		gitCmd.OSCommand.command = s.command
-		s.test(gitCmd.Show(s.arg))
-	}
-}
-
 // TestGitCommandCheckout is a function.
 func TestGitCommandCheckout(t *testing.T) {
 	type scenario struct {
@@ -1523,7 +1448,7 @@ func TestGitCommandGetBranchGraph(t *testing.T) {
 	gitCmd := NewDummyGitCommand()
 	gitCmd.OSCommand.command = func(cmd string, args ...string) *exec.Cmd {
 		assert.EqualValues(t, "git", cmd)
-		assert.EqualValues(t, []string{"log", "--graph", "--color", "--abbrev-commit", "--decorate", "--date=relative", "--pretty=medium", "-100", "test"}, args)
+		assert.EqualValues(t, []string{"log", "--graph", "--color", "--abbrev-commit", "--decorate", "--date=relative", "--pretty=medium", "test"}, args)
 
 		return exec.Command("echo")
 	}
diff --git a/pkg/gui/branches_panel.go b/pkg/gui/branches_panel.go
index 1bf408026..ff77c9cb4 100644
--- a/pkg/gui/branches_panel.go
+++ b/pkg/gui/branches_panel.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/fatih/color"
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands"
 	"github.com/jesseduffield/lazygit/pkg/utils"
@@ -37,40 +36,45 @@ func (gui *Gui) handleBranchSelect(g *gocui.Gui, v *gocui.View) error {
 
 	// This really shouldn't happen: there should always be a master branch
 	if len(gui.State.Branches) == 0 {
-		return gui.renderString(g, "main", gui.Tr.SLocalize("NoBranchesThisRepo"))
+		return gui.newStringTask("main", gui.Tr.SLocalize("NoBranchesThisRepo"))
 	}
 	branch := gui.getSelectedBranch()
 	if err := gui.focusPoint(0, gui.State.Panels.Branches.SelectedLine, len(gui.State.Branches), v); err != nil {
 		return err
 	}
-	go func() {
-		_ = gui.RenderSelectedBranchUpstreamDifferences()
-	}()
-	go func() {
-		upstream, _ := gui.GitCommand.GetUpstreamForBranch(branch.Name)
-		if strings.Contains(upstream, "no upstream configured for branch") || strings.Contains(upstream, "unknown revision or path not in the working tree") {
-			upstream = gui.Tr.SLocalize("notTrackingRemote")
-		}
-		graph, err := gui.GitCommand.GetBranchGraph(branch.Name)
-		if err != nil && strings.HasPrefix(graph, "fatal: ambiguous argument") {
-			graph = gui.Tr.SLocalize("NoTrackingThisBranch")
-		}
-		_ = gui.renderString(g, "main", fmt.Sprintf("%s → %s\n\n%s", utils.ColoredString(branch.Name, color.FgGreen), utils.ColoredString(upstream, color.FgRed), graph))
-	}()
+	if err := gui.RenderSelectedBranchUpstreamDifferences(); err != nil {
+		return err
+	}
+
+	cmd := gui.OSCommand.ExecutableFromString(
+		gui.GitCommand.GetBranchGraphCmdStr(branch.Name),
+	)
+	if err := gui.newCmdTask("main", cmd); err != nil {
+		gui.Log.Error(err)
+	}
 	return nil
 }
 
 func (gui *Gui) RenderSelectedBranchUpstreamDifferences() error {
-	// here we tell the selected branch that it is selected.
-	// this is necessary for showing stats on a branch that is selected, because
-	// the displaystring function doesn't have access to gui state to tell if it's selected
-	for i, branch := range gui.State.Branches {
-		branch.Selected = i == gui.State.Panels.Branches.SelectedLine
-	}
+	return gui.newTask("branches", func(stop chan struct{}) error {
+		// here we tell the selected branch that it is selected.
+		// this is necessary for showing stats on a branch that is selected, because
+		// the displaystring function doesn't have access to gui state to tell if it's selected
+		for i, branch := range gui.State.Branches {
+			branch.Selected = i == gui.State.Panels.Branches.SelectedLine
+		}
 
-	branch := gui.getSelectedBranch()
-	branch.Pushables, branch.Pullables = gui.GitCommand.GetBranchUpstreamDifferenceCount(branch.Name)
-	return gui.renderListPanel(gui.getBranchesView(), gui.State.Branches)
+		branch := gui.getSelectedBranch()
+		branch.Pushables, branch.Pullables = gui.GitCommand.GetBranchUpstreamDifferenceCount(branch.Name)
+
+		select {
+		case <-stop:
+			return nil
+		default:
+		}
+
+		return gui.renderListPanel(gui.getBranchesView(), gui.State.Branches)
+	})
 }
 
 // gui.refreshStatus is called at the end of this because that's when we can
diff --git a/pkg/gui/commit_files_panel.go b/pkg/gui/commit_files_panel.go
index 1dee4a3cd..42afc6c94 100644
--- a/pkg/gui/commit_files_panel.go
+++ b/pkg/gui/commit_files_panel.go
@@ -43,11 +43,15 @@ func (gui *Gui) handleCommitFileSelect(g *gocui.Gui, v *gocui.View) error {
 	if err := gui.focusPoint(0, gui.State.Panels.CommitFiles.SelectedLine, len(gui.State.CommitFiles), v); err != nil {
 		return err
 	}
-	commitText, err := gui.GitCommand.ShowCommitFile(commitFile.Sha, commitFile.Name, false)
-	if err != nil {
-		return err
+
+	cmd := gui.OSCommand.ExecutableFromString(
+		gui.GitCommand.ShowCommitFileCmdStr(commitFile.Sha, commitFile.Name, false),
+	)
+	if err := gui.newCmdTask("main", cmd); err != nil {
+		gui.Log.Error(err)
 	}
-	return gui.renderString(g, "main", commitText)
+
+	return nil
 }
 
 func (gui *Gui) handleSwitchToCommitsPanel(g *gocui.Gui, v *gocui.View) error {
diff --git a/pkg/gui/commits_panel.go b/pkg/gui/commits_panel.go
index 32672a40b..abc6b47ec 100644
--- a/pkg/gui/commits_panel.go
+++ b/pkg/gui/commits_panel.go
@@ -53,7 +53,7 @@ func (gui *Gui) handleCommitSelect(g *gocui.Gui, v *gocui.View) error {
 
 	commit := gui.getSelectedCommit(g)
 	if commit == nil {
-		return gui.renderString(g, "main", gui.Tr.SLocalize("NoCommitsThisBranch"))
+		return gui.newStringTask("main", gui.Tr.SLocalize("NoCommitsThisBranch"))
 	}
 
 	if err := gui.focusPoint(0, gui.State.Panels.Commits.SelectedLine, len(gui.State.Commits), v); err != nil {
@@ -65,11 +65,14 @@ func (gui *Gui) handleCommitSelect(g *gocui.Gui, v *gocui.View) error {
 		return nil
 	}
 
-	commitText, err := gui.GitCommand.Show(commit.Sha)
-	if err != nil {
-		return err
+	cmd := gui.OSCommand.ExecutableFromString(
+		gui.GitCommand.ShowCmdStr(commit.Sha),
+	)
+	if err := gui.newCmdTask("main", cmd); err != nil {
+		gui.Log.Error(err)
 	}
-	return gui.renderString(g, "main", commitText)
+
+	return nil
 }
 
 func (gui *Gui) refreshCommits(g *gocui.Gui) error {
@@ -463,7 +466,7 @@ func (gui *Gui) handleToggleDiffCommit(g *gocui.Gui, v *gocui.View) error {
 	// get selected commit
 	commit := gui.getSelectedCommit(g)
 	if commit == nil {
-		return gui.renderString(g, "main", gui.Tr.SLocalize("NoCommitsThisBranch"))
+		return gui.newStringTask("main", gui.Tr.SLocalize("NoCommitsThisBranch"))
 	}
 
 	// if already selected commit delete
@@ -486,7 +489,7 @@ func (gui *Gui) handleToggleDiffCommit(g *gocui.Gui, v *gocui.View) error {
 			return gui.createErrorPanel(gui.g, err.Error())
 		}
 
-		return gui.renderString(g, "main", commitText)
+		return gui.newStringTask("main", commitText)
 	}
 
 	return nil
diff --git a/pkg/gui/files_panel.go b/pkg/gui/files_panel.go
index 38622efa1..47e7bae1f 100644
--- a/pkg/gui/files_panel.go
+++ b/pkg/gui/files_panel.go
@@ -32,7 +32,7 @@ func (gui *Gui) selectFile(alreadySelected bool) error {
 		if err != gui.Errors.ErrNoFiles {
 			return err
 		}
-		return gui.renderString(gui.g, "main", gui.Tr.SLocalize("NoChangedFiles"))
+		return gui.newStringTask("main", gui.Tr.SLocalize("NoChangedFiles"))
 	}
 
 	if err := gui.focusPoint(0, gui.State.Panels.Files.SelectedLine, len(gui.State.Files), gui.getFilesView()); err != nil {
@@ -45,37 +45,40 @@ func (gui *Gui) selectFile(alreadySelected bool) error {
 		return gui.refreshMergePanel()
 	}
 
-	content := gui.GitCommand.Diff(file, false, false)
-	contentCached := gui.GitCommand.Diff(file, false, true)
-	leftContent := content
+	if !alreadySelected {
+		if err := gui.resetOrigin(gui.getMainView()); err != nil {
+			return err
+		}
+		if err := gui.resetOrigin(gui.getSecondaryView()); err != nil {
+			return err
+		}
+	}
+
 	if file.HasStagedChanges && file.HasUnstagedChanges {
 		gui.State.SplitMainPanel = true
 		gui.getMainView().Title = gui.Tr.SLocalize("UnstagedChanges")
 		gui.getSecondaryView().Title = gui.Tr.SLocalize("StagedChanges")
+		cmdStr := gui.GitCommand.DiffCmdStr(file, false, true)
+		cmd := gui.OSCommand.ExecutableFromString(cmdStr)
+		if err := gui.newCmdTask("secondary", cmd); err != nil {
+			return err
+		}
 	} else {
 		gui.State.SplitMainPanel = false
 		if file.HasUnstagedChanges {
-			leftContent = content
 			gui.getMainView().Title = gui.Tr.SLocalize("UnstagedChanges")
 		} else {
-			leftContent = contentCached
 			gui.getMainView().Title = gui.Tr.SLocalize("StagedChanges")
 		}
 	}
 
-	if alreadySelected {
-		gui.g.Update(func(*gocui.Gui) error {
-			if err := gui.setViewContent(gui.g, gui.getSecondaryView(), contentCached); err != nil {
-				return err
-			}
-			return gui.setViewContent(gui.g, gui.getMainView(), leftContent)
-		})
-		return nil
-	}
-	if err := gui.renderString(gui.g, "secondary", contentCached); err != nil {
+	cmdStr := gui.GitCommand.DiffCmdStr(file, false, !file.HasUnstagedChanges && file.HasStagedChanges)
+	cmd := gui.OSCommand.ExecutableFromString(cmdStr)
+	if err := gui.newCmdTask("main", cmd); err != nil {
 		return err
 	}
-	return gui.renderString(gui.g, "main", leftContent)
+
+	return nil
 }
 
 func (gui *Gui) refreshFiles() error {
@@ -369,15 +372,15 @@ func (gui *Gui) catSelectedFile(g *gocui.Gui) (string, error) {
 		if err != gui.Errors.ErrNoFiles {
 			return "", err
 		}
-		return "", gui.renderString(g, "main", gui.Tr.SLocalize("NoFilesDisplay"))
+		return "", gui.newStringTask("main", gui.Tr.SLocalize("NoFilesDisplay"))
 	}
 	if item.Type != "file" {
-		return "", gui.renderString(g, "main", gui.Tr.SLocalize("NotAFile"))
+		return "", gui.newStringTask("main", gui.Tr.SLocalize("NotAFile"))
 	}
 	cat, err := gui.GitCommand.CatFile(item.Name)
 	if err != nil {
 		gui.Log.Error(err)
-		return "", gui.renderString(g, "main", err.Error())
+		return "", gui.newStringTask("main", err.Error())
 	}
 	return cat, nil
 }
diff --git a/pkg/gui/gui.go b/pkg/gui/gui.go
index 2bdb66e0f..d748b4d72 100644
--- a/pkg/gui/gui.go
+++ b/pkg/gui/gui.go
@@ -25,6 +25,7 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/commands"
 	"github.com/jesseduffield/lazygit/pkg/config"
 	"github.com/jesseduffield/lazygit/pkg/i18n"
+	"github.com/jesseduffield/lazygit/pkg/tasks"
 	"github.com/jesseduffield/lazygit/pkg/theme"
 	"github.com/jesseduffield/lazygit/pkg/updates"
 	"github.com/jesseduffield/lazygit/pkg/utils"
@@ -68,20 +69,21 @@ type Teml i18n.Teml
 
 // Gui wraps the gocui Gui object which handles rendering and events
 type Gui struct {
-	g             *gocui.Gui
-	Log           *logrus.Entry
-	GitCommand    *commands.GitCommand
-	OSCommand     *commands.OSCommand
-	SubProcess    *exec.Cmd
-	State         guiState
-	Config        config.AppConfigurer
-	Tr            *i18n.Localizer
-	Errors        SentinelErrors
-	Updater       *updates.Updater
-	statusManager *statusManager
-	credentials   credentials
-	waitForIntro  sync.WaitGroup
-	fileWatcher   *fileWatcher
+	g                    *gocui.Gui
+	Log                  *logrus.Entry
+	GitCommand           *commands.GitCommand
+	OSCommand            *commands.OSCommand
+	SubProcess           *exec.Cmd
+	State                guiState
+	Config               config.AppConfigurer
+	Tr                   *i18n.Localizer
+	Errors               SentinelErrors
+	Updater              *updates.Updater
+	statusManager        *statusManager
+	credentials          credentials
+	waitForIntro         sync.WaitGroup
+	fileWatcher          *fileWatcher
+	viewBufferManagerMap map[string]*tasks.ViewBufferManager
 }
 
 // for now the staging panel state, unlike the other panel states, is going to be
@@ -229,14 +231,15 @@ func NewGui(log *logrus.Entry, gitCommand *commands.GitCommand, oSCommand *comma
 	}
 
 	gui := &Gui{
-		Log:           log,
-		GitCommand:    gitCommand,
-		OSCommand:     oSCommand,
-		State:         initialState,
-		Config:        config,
-		Tr:            tr,
-		Updater:       updater,
-		statusManager: &statusManager{},
+		Log:                  log,
+		GitCommand:           gitCommand,
+		OSCommand:            oSCommand,
+		State:                initialState,
+		Config:               config,
+		Tr:                   tr,
+		Updater:              updater,
+		statusManager:        &statusManager{},
+		viewBufferManagerMap: map[string]*tasks.ViewBufferManager{},
 	}
 
 	gui.watchFilesForChanges()
@@ -261,8 +264,14 @@ func (gui *Gui) scrollDownView(viewName string) error {
 		_, sy := mainView.Size()
 		y += sy
 	}
+	scrollHeight := gui.Config.GetUserConfig().GetInt("gui.scrollHeight")
 	if y < len(mainView.BufferLines()) {
-		return mainView.SetOrigin(ox, oy+gui.Config.GetUserConfig().GetInt("gui.scrollHeight"))
+		if err := mainView.SetOrigin(ox, oy+scrollHeight); err != nil {
+			return err
+		}
+	}
+	if manager, ok := gui.viewBufferManagerMap[viewName]; ok {
+		manager.ReadLines(scrollHeight)
 	}
 	return nil
 }
@@ -465,7 +474,23 @@ func (gui *Gui) layout(g *gocui.Gui) error {
 		secondary = "main"
 	}
 
-	v, err := g.SetView(main, leftSideWidth+panelSpacing, 0, panelSplitX, height-2, gocui.LEFT)
+	// reading more lines into main view buffers upon resize
+	mainHeight := height - 2
+	prevMainView, err := gui.g.View("main")
+	if err == nil {
+		_, prevMainHeight := prevMainView.Size()
+		heightDiff := mainHeight - 1 - prevMainHeight
+		if heightDiff > 0 {
+			if manager, ok := gui.viewBufferManagerMap["main"]; ok {
+				manager.ReadLines(heightDiff)
+			}
+			if manager, ok := gui.viewBufferManagerMap["secondary"]; ok {
+				manager.ReadLines(heightDiff)
+			}
+		}
+	}
+
+	v, err := g.SetView(main, leftSideWidth+panelSpacing, 0, panelSplitX, mainHeight, gocui.LEFT)
 	if err != nil {
 		if err.Error() != "unknown view" {
 			return err
@@ -479,7 +504,7 @@ func (gui *Gui) layout(g *gocui.Gui) error {
 	if !gui.State.SplitMainPanel {
 		hiddenViewOffset = 9999
 	}
-	secondaryView, err := g.SetView(secondary, panelSplitX+1+hiddenViewOffset, hiddenViewOffset, width-1+hiddenViewOffset, height-2+hiddenViewOffset, gocui.LEFT)
+	secondaryView, err := g.SetView(secondary, panelSplitX+1+hiddenViewOffset, hiddenViewOffset, width-1+hiddenViewOffset, mainHeight+hiddenViewOffset, gocui.LEFT)
 	if err != nil {
 		if err.Error() != "unknown view" {
 			return err
@@ -843,6 +868,11 @@ func (gui *Gui) Run() error {
 func (gui *Gui) RunWithSubprocesses() error {
 	for {
 		if err := gui.Run(); err != nil {
+			for _, manager := range gui.viewBufferManagerMap {
+				manager.Close()
+			}
+			gui.viewBufferManagerMap = map[string]*tasks.ViewBufferManager{}
+
 			if err == gocui.ErrQuit {
 				if !gui.State.RetainOriginalDir {
 					if err := gui.recordCurrentDirectory(); err != nil {
diff --git a/pkg/gui/merge_panel.go b/pkg/gui/merge_panel.go
index 25238ce4f..4b86cf6c0 100644
--- a/pkg/gui/merge_panel.go
+++ b/pkg/gui/merge_panel.go
@@ -212,7 +212,7 @@ func (gui *Gui) refreshMergePanel() error {
 	if err != nil {
 		return err
 	}
-	if err := gui.renderString(gui.g, "main", content); err != nil {
+	if err := gui.newStringTask("main", content); err != nil {
 		return err
 	}
 	if err := gui.scrollToConflict(gui.g); err != nil {
diff --git a/pkg/gui/reflog_panel.go b/pkg/gui/reflog_panel.go
index 33577c073..e766070fb 100644
--- a/pkg/gui/reflog_panel.go
+++ b/pkg/gui/reflog_panel.go
@@ -31,17 +31,20 @@ func (gui *Gui) handleReflogCommitSelect(g *gocui.Gui, v *gocui.View) error {
 
 	commit := gui.getSelectedReflogCommit()
 	if commit == nil {
-		return gui.renderString(g, "main", "No reflog history")
+		return gui.newStringTask("main", "No reflog history")
 	}
 	if err := gui.focusPoint(0, gui.State.Panels.ReflogCommits.SelectedLine, len(gui.State.ReflogCommits), v); err != nil {
 		return err
 	}
 
-	commitText, err := gui.GitCommand.Show(commit.Sha)
-	if err != nil {
-		return err
+	cmd := gui.OSCommand.ExecutableFromString(
+		gui.GitCommand.ShowCmdStr(commit.Sha),
+	)
+	if err := gui.newCmdTask("main", cmd); err != nil {
+		gui.Log.Error(err)
 	}
-	return gui.renderString(g, "main", commitText)
+
+	return nil
 }
 
 func (gui *Gui) refreshReflogCommits() error {
diff --git a/pkg/gui/remote_branches_panel.go b/pkg/gui/remote_branches_panel.go
index 4b8658df7..fbe299fd9 100644
--- a/pkg/gui/remote_branches_panel.go
+++ b/pkg/gui/remote_branches_panel.go
@@ -2,12 +2,9 @@ package gui
 
 import (
 	"fmt"
-	"strings"
 
-	"github.com/fatih/color"
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands"
-	"github.com/jesseduffield/lazygit/pkg/utils"
 )
 
 // list panel functions
@@ -37,7 +34,7 @@ func (gui *Gui) handleRemoteBranchSelect(g *gocui.Gui, v *gocui.View) error {
 	remote := gui.getSelectedRemote()
 	remoteBranch := gui.getSelectedRemoteBranch()
 	if remoteBranch == nil {
-		return gui.renderString(g, "main", "No branches for this remote")
+		return gui.newStringTask("main", "No branches for this remote")
 	}
 
 	gui.focusPoint(0, gui.State.Panels.Menu.SelectedLine, gui.State.MenuItemCount, v)
@@ -45,13 +42,14 @@ func (gui *Gui) handleRemoteBranchSelect(g *gocui.Gui, v *gocui.View) error {
 		return err
 	}
 
-	go func() {
-		graph, err := gui.GitCommand.GetBranchGraph(fmt.Sprintf("%s/%s", remote.Name, remoteBranch.Name))
-		if err != nil && strings.HasPrefix(graph, "fatal: ambiguous argument") {
-			graph = gui.Tr.SLocalize("NoTrackingThisBranch")
-		}
-		_ = gui.renderString(g, "main", fmt.Sprintf("%s/%s\n\n%s", utils.ColoredString(remote.Name, color.FgRed), utils.ColoredString(remoteBranch.Name, color.FgGreen), graph))
-	}()
+	branchName := fmt.Sprintf("%s/%s", remote.Name, remoteBranch.Name)
+
+	cmd := gui.OSCommand.ExecutableFromString(
+		gui.GitCommand.GetBranchGraphCmdStr(branchName),
+	)
+	if err := gui.newCmdTask("main", cmd); err != nil {
+		gui.Log.Error(err)
+	}
 
 	return nil
 }
diff --git a/pkg/gui/remotes_panel.go b/pkg/gui/remotes_panel.go
index a646462d9..ca3e3aae1 100644
--- a/pkg/gui/remotes_panel.go
+++ b/pkg/gui/remotes_panel.go
@@ -36,13 +36,13 @@ func (gui *Gui) handleRemoteSelect(g *gocui.Gui, v *gocui.View) error {
 
 	remote := gui.getSelectedRemote()
 	if remote == nil {
-		return gui.renderString(g, "main", "No remotes")
+		return gui.newStringTask("main", "No remotes")
 	}
 	if err := gui.focusPoint(0, gui.State.Panels.Remotes.SelectedLine, len(gui.State.Remotes), v); err != nil {
 		return err
 	}
 
-	return gui.renderString(g, "main", fmt.Sprintf("%s\nUrls:\n%s", utils.ColoredString(remote.Name, color.FgGreen), strings.Join(remote.Urls, "\n")))
+	return gui.newStringTask("main", fmt.Sprintf("%s\nUrls:\n%s", utils.ColoredString(remote.Name, color.FgGreen), strings.Join(remote.Urls, "\n")))
 }
 
 func (gui *Gui) refreshRemotes() error {
diff --git a/pkg/gui/stash_panel.go b/pkg/gui/stash_panel.go
index 8ccdc9880..23ecaba60 100644
--- a/pkg/gui/stash_panel.go
+++ b/pkg/gui/stash_panel.go
@@ -34,16 +34,19 @@ func (gui *Gui) handleStashEntrySelect(g *gocui.Gui, v *gocui.View) error {
 
 	stashEntry := gui.getSelectedStashEntry(v)
 	if stashEntry == nil {
-		return gui.renderString(g, "main", gui.Tr.SLocalize("NoStashEntries"))
+		return gui.newStringTask("main", gui.Tr.SLocalize("NoStashEntries"))
 	}
 	if err := gui.focusPoint(0, gui.State.Panels.Stash.SelectedLine, len(gui.State.StashEntries), v); err != nil {
 		return err
 	}
-	go func() {
-		// doing this asynchronously cos it can take time
-		diff, _ := gui.GitCommand.GetStashEntryDiff(stashEntry.Index)
-		_ = gui.renderString(g, "main", diff)
-	}()
+
+	cmd := gui.OSCommand.Executable